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THE ELEMENTS 



OF 



PHYSICAL GEOGRAPHY 



BY 

EDWIN J. HOUSTON, A.M., Ph.D. 

n 

EMERITUS PROFESSOR OF PHYSICAL GEOGRAPHY AND NATURAL PHILOSOPHY 

IN THE CENTRAL HIGH SCHOOL OF PHILADELPHIA; PROFESSOR 

OF PHYSICS IN THE FRANKLIN INSTITUTE OF 

THE STATE OF PENNSYLVANIA 



COMPLETELY REVISED BY 

THOS. H. HUGHES 

TEACHER IN EVANDER CHILDS HIGH SCHOOL, NEW YORK CITY 
AUTHOR OF " A BRIEF PHYSICAL GEOGRAPHY " AND " A BRIEF COMMERCIAL 

GEOGRAPHY " 



HINDS, NOBLE & ELDREDGE 

NEW YORK AND PHILADELPHIA 



.H? 



Copyright, 1901, by Eldredge & Brother. 
Copyright, 1916, by Hinds, Noble & Eldredge. 



MAR 30 1916 



5)CI,A427466 



PREFACE. 



In the preparation of this work, an endeavor has been made to 
supply a concise yet comprehensive text-book, suited to the wants 
of a majority of our schools. 

The Author, in the course of his teaching, has experienced the 
need of a work in which unnecessary details should be suppressed, 
and certain subjects added, which, though usually omitted in works 
on Physical Geography, seem, in his judgment, to belong properly 
to the science. The variety of topics necessarily included under 
the head of Physical Geography renders it almost impossible to 
cover the entire ground of the ordinary text-books during the time 
which most schools are able to devote to the study, and the feeling 
of incompleted work thus impressed on the mind of both teacher 
and scholar is of the most discouraging nature. 

To remove these difficulties, the author, during the past few years, 
has arranged for his own students a course of study, which, with a 
few modifications, he has at last put into book form, thinking that 
it may prove beneficial to others. 

The division of the text into large and small print has been made 
with a view of meeting the wants of different grades of schools, the 
large type containing only the more important statements, and the 
small type being especially designed for the use of the teacher and 
the advanced student. The maps have been carefully drawn by the 
author according to the standard works and the latest authorities. 
Neither time nor expense has been spared to insure accuracy of 
detail and clearness of delineation. 

Throughout the work no pains have been spared to insure strict 
accuracy of statement. Clearness and conciseness have been par- 



vi PREFACE. 

ticularly aimed at ; for which reason the names of authorities for 
statements which are now generally credited have been purposely 
omitted. 

The Author has not hesitated to draw information from all the 
standard works on Geography, Physics, Geology, Astronomy, and 
other allied sciences ; and in the compilation of the Pronouncing 
"^^ocabulary he acknowledges his indebtedness to Lippincott's Gaz- 
etteer of the World. 

Acknowledgments are due to Mr. W. M. Spackman, of Phila- 
delphia, and Prof. Elihu Thomson, of the Central High School, 
for critical review of the manuscript. Also to Mr. M. Benjamin 
Snyder, of the Central High School, for revision of the proof-sheets 

of the chapter on Mathematical Geography. 

E. J. H. 
Central High School, Philadelphia, Pa. 



PREFACE TO THE REVISED EDITION. 



Houston's Elements of Physical Geography has now been before 
the teaching public for more than a quarter of a century. During 
that time, in order to keep abreast with advances in the many 
separate physical sciences that are necessarily embraced under the 
wide scope of Physical Geography, many new editions of the book 
have been issued. 

But the advances, during comparatively recent years, have been so 
marked that at the earnest request of teachers from all parts of the 
country the author has prepared a new book, based on the general 
lines of the old work, but practically rewritten. 

For convenience, the shape of the new book has been changed to 
a duodecimo, the size of the maps, however, being retained, by 
making them occupy the space of two pages, across which inserts 
are made. 



PREFACE. vii 

In the preparation of the new book the author has endeavored so 
to proportion the subject matter as to give due prominence to such 
topics as, in his judgment, would prove of greatest value to the 
student. In this direction physiography has been treated more 
fully than in the older book. At the same time, however, he has 
studiously avoided giving such an undue prominence to this part of 
the science as would necessitate the suppression of equally important 
topics. The influence of geological agencies in giving the earth its 
present surface features has been fully treated, and yet not so fully 
as practically to exclude the influences of these features on the 
climate, and this, in its turn, on vegetable and animal life, especially 
on the development and civilization of earth's highest type of life, 
man. 

As in the old book, the logical order of sequence of topics has 
been carefully considered, since in this manner only can the best 
results be achieved during actual work in the school-room. 

The author has not hesitated to draw, information from all 
standard works on Geography, Physics, Astronomy, Geology, 
Botany, Zoology, and other allied sciences. He acknowledges his 
indebtedness to many of his teaching friends throughout the country 
for valuable suggestions as to the subject matter, etc., of the new 
book. Especially is he indebted to his friends, Prof. B. W. Mitchell 
for careful reading of the proof-sheets of the book, Prof. Charles S. 
Dolley for valuable suggestions, and Prof. Angelo Heilprin for a 
careful reading of the proof-sheets on Zoological Geography. 

The author offers the new book to the teaching fraternity in the 
hope that it will prove of service to them in teaching this exceed- 
ingly attractive study. 

The Author, 



CONTENTS. 



-»o>»4c 



Inteodxjctoby 11 

PART L 

THE EARTH AS A PLANET. 

CHAPTER PAGE 

I. Mathematical Geography ... 13 

PART II. 

THE LAND. 

SECTION I.— The Inside of the 
Earth. 

I. The Heated Interior 40 

II. Volcanoes 44 

III. Earthquakes 55 

SECTION II.— The Outside of the 
Earth. 

I. The Crust of the Earth ... 63 

II. Distribution of the Land Areas 77 

III. Islands 83 

IV. Eelief Forms of the Land . . 91 
V. Eelief Forms of the Continents 100 

PART III. 

THE "WATER. 

SECTION I.— Continental Waters. 

I. Physical Properties of Water . 123 

II. Drainage 128 

III. Eivers 136 

IV. Work of Eivers 142 

V. Drainage Systems 149 

VI. Lakes 152 

viii 



SECTION II.— Oceanic "Waters. 

CHAPTER PAGE 

I. The Ocean .162 

II. Oceanic Movements 168 

III. Ocean Currents 177 

PART IV. 

THE ATMOSPHERE. 

SECTION I.— The Atmosphere. 
I. General Properties of the At- 
mosphere 187 

II. aimate .193 

III. The Winds 201 

IV. Storms 209 

SECTION II.— Moisture of the 
Atmosphere. 

I. Precipitation of Moisture . 22] 
II. Hail, Snow, and Glaciers ... 236 
III. Electrical and Optical Phenom- 
ena 250 

PART V. 

PLANT LIFE, ANIMAL LIFE, 
AND MINERALS. 

SECTION I.— Plant Life. 

I. Plant Geography 267 

II. Cultivated Plants 281 

SECTION II.— Animal Life. 
I. Zoological Geography .... 290 
II. The Distribution of the Human 

Eace 306 



CONTENTS. 



IX 



SECTION III.— Minerals. 

CHAPTER PAGE 

I. Minerals 319 

PART VL 

THE PHYSICAL FEATURES OF 
THE UNITED STATES. 

I, Surface Structure 334 

II. Meteorology 339 

*II, Vegetable and Animal Life . 346 



I CHAPTER PAGE 

IV. Agricultural and Mineral Pro- 
ductions ... 349 

V. Alaska 355 

VI. The Insular Possessions of the 

United States 358 

Genekal Syllabus . 372 

General Review Questions . . 378 

General Map Questions .... 381 

Index ' 386 



o»<c 



INDEX TO THE MAPS. 

between pages 

Map of Volcanoes and Eegions of Earthquakes 58- 59 

Map Showing Geological Formation of the Earth 66- 67 

Map of Oceanic Basins, Areas, and Eiver-systems 142-143 

Map of the Ocean Currents 168-169 

Map of the Isothermal Lines 197a-197b 

Map of the Winds and Ocean Eoutes 202-203 

Map Showing the Distribution of Vegetation 278-279 

Map Showing the Distribution of Animals 292-293 

Map Showing the Distribution of the Eaces of Men ..... 308-309 

Physical Map of the United States 332-333 

Map Showing Tracks of Storm-centres, Areas of Low Barom- 
eter, Weather Signals, and Storm Signals 344-345 




Yosemite Valley, California. A Glaciated Valley 3,000 Feet Deep in Granite Bock. 



THE ELEMENTS 

OF 

PHYSICAL GEOGRAPHY. 



INTRODUCTORY, 

1. Geography is a description of the earth. 

The earth may be described in three different ways : 

(1) In its relations to the solar system ; 

(2) In its relations to government and society ; 

(3) In its relations to nature. 

Hence arise three branches of geography — Mathematical, Polit- 
ical, and Physical. 

2. Mathematical Geography treats of the earth in its relations 
to the solar system. 

Mathematical Geograpliy forms the true hasis for accurate geographical 
study. Here we learn the location of the earth in space, its relations to the 
other members of the solar system, its size, form, and movements, its division 
by imaginary lines, and the methods of representing all or portions of its surface 
on maps. 

3. Political Geography treats of the earth in its relations to 
the governments and societies of men, of the manner of life of a 
people, and of their civilization and government. 

4. Physical Geography treats of the earth in its relations to 
nature and to the natural laws which determine its phenomena. 
It treats especially of the systematic distribution of all animate 
and inanimate objects found on the earth's surface. It not only 

11 



12 PHYSICAL GEOGRAPHY. 

tells of their presence in a given locality, but it also endeavors to 
discover the causes and effects of their existence. 

Physical Geography therefore treats of the distribution of Land, 

Water, Air, Plants, Animals, and Minerals. 

Geography deals with the inside as well as with the outside of the earth. It 
encroaches here on the province of geology. Both treat of the earth : geography 
mainly with the earth's present condition ; geology with its condition both in 
the past and present. 

Some authors make physical geography a branch of geology, and call it phys- 
iographic geology or physiography, but the term "physical," or, as etymology 
would make it, "natural" geography is preferable. 

A separate branch of geography, called Commercial Geography, is based on a 
combination of portions of physical and political geography. As the name indi- 
cates, commercial geography is such a description of the surface of the earth as 
includes the production, transportation, and interchange of commodities, either 
as raw or as manufactured materials. 



PART I. 
THE EARTH AS A PLANET. 

CHAPTER I. 
Mathematical Geography. 

5. The Earth moves through empty space around the sun. 

A book or other inanimate object placed on a support will remain 

at rest until something moves it. If the book were thrown up into 

the air it would keep on moving upward unless some cause occurred 

to stop it. That property of matter by which it retains its state of 

rest or its state of motion, unless some cause occurs to change that 

state, is called inertia. 

The book when thrown up into the air soon stops moving upward and falls 
to the earth ; because — • 

(1) The earth draws or attracts it ; 

(2) The moving body gives some of its motion to the air through which it 
moves. 

Were the book thrown in any direction through the empty space in which 
the stars move, it would continue moving in that direction for ever, unless it 
came near to some other body which would attract it and cause it to change 
its motion. 

Our earth moves through empty space on account of its inertia, 
and must continue so moving for ever. All heavenly bodies con- 
tinue their motion solely on account of their inertia. 

Space is not absolutely empty, but is everywhere filled with a very tenuous 
substance called ether, which transmits to us the light and heat of the heavenly 
bodies. Wherever the telescope reveals the presence of stars we must believe the 
ether also extends. 

13 



14 PHYSICAL GEOGRAPHY. 

6. The Stars. — The numerous points of light that appear in 
the heavens, on clear, moonless nights, are called stars. Stars consist 
of immense balls of matter, that, like our earth, are moving through 
empty space. A few of these brilliant bodies, apparently stars, are 
planets. Planets differ from other stars in appearance, since they do 
not perceptibly twinkle; moreover, the planets shine not because of 
their own light, but by light thrown on them from the sun. The 
planets move around the sun and so change their positions as regards 
the other stars, which always retain, approximately, the same rela- 
tive positions, and are, therefore, frequently called fixed stars, 
although, as already stated, they are moving through empty space. 

Our sun is believed to be one of the fixed stars, and, immense 
though it be, is, nevertheless, far smaller than many of them. 

The fixed stars, like our sun, are highly heated and shine by means of the 
light they throw off in all directions. Many of them are more highly heated 
than our sun. Others again are less highly heated, and still others are dark, 
or do not shine at all, being too cold to emit light. 

The actual number of stars that can be seen by the unassisted eye, under 
favorable conditions, is probably about 7000. An ordinary opera-glass, however, 
increases this number to about 100,000. A telescope, whose larger glass is about 
2i inches across, increases this number to about 300,000, while the great Lick 
telescope brings it to about 100,000,000. 

It is possible that in the remote realms of space are countless stars whose 
distances are too great to permit them to be seen by even the most powerful 
telescopes. There are, moreover, numerous dark bodies, or suns, that have 
completely cooled, thus again greatly increasing the number of the heavenly 
bodies. 

7. The Solar System comprises the sun, eight large bodies 
called planets, and upward of four hundred and sixty smaller 
bodies called planetoids or asteroids, besides numerous comets and 
meteors. Some of the planets have bodies called moons or satellites 
moving around them. These also belong to the solar system. 

Fig. 1, represents the solar system. In the centre is the sun. 
The circles drawn around the sun show the paths or orbits of the 
planets. These orbits are represented as circular, but in reality 
they are slightly flattened or elliptical. The elongated orbits mark 
the paths of the comets. The drawing shows the relative sizes of 



MATHEMATICAL GEOGRAPHY. 



15 



the planets and their order from the sun, their common cen- 
tre. 

8. Names of the Planets. — The planets, named in their regular 
order from the sun, are : Mercury, Venus, Earth, Mars, Jupiter, 
Saturn, Uranus, and Neptune. The first four — Mercury, Venus, 




Fig. 1.— Tlie Solar System. 

Earth, and Mars — are comparatively small ; the second four — ■ 
Jupiter, Saturn, Uranus, and Neptune — are very large. The initial 
letters of the last three planets, Saturn, Uranus, and Neptune, 
taken in their order from the sun : s, u, and n — spell the name 
of their common centre. 



16 



PHYSICAL GEOGRAPHY. 



Data Concerning the Solar System. 



Names. 



Diameter. 



Actual, in 
miles. 



Relative, 
Earth = 1. 



Distance from sun 

in round numbers 

—miles. 



Sun . . 
Jupiter . 
Saturn . 
Neptune 
Ui"anus . 
Earth . 
Venus . 
Mai-s . . 
Mercury 
Moon . 

Asteroids 



866,500 

86,500 

71,000 

34,800 

31,900 

7,918 

7,770 

4,230 

3,000 

2,163 

From a few 

miles to 500 



}• 



109.43 
10.94 
8.97 
4.39 
4.03 
1. 
.98 
.52 
.378 
.273 



92,900,000* 

483,300,000 

886,000,000 

2,791,600,000 

1,781,900,000 

92,900,000 

67,200,000 

141,500,000 

36,000,000 

238,818* 



* Mean distance from Earth. 

The asteroids are mostly found in the space between Mars and Jupiter. It is 
probable that all these bodies were once collected in a ring around the central 
nebulous sun, but that this ring failed to collect in a single planet, owing to 
the presence of the large planet Jupiter, whose powerful attraction tore the 
ring into the separate fragments that now form the asteroids. 

It is difficult to obtain clear conceptions of distances that are represented by 
millions of miles. Should a man travel forty times around the earth at the 
equator he would have gone over only about 1,000,000 miles. ZSTow, Mercury, 
the nearest of the planets, is thirty-six times farther from the sun than the entire 
distance the man would have travelled, while Neptune is nearly three thousand 
times the distance he would have travelled. 

In estimating the enormous distances of the fixed stars it is convenient to 
use for our unit of measurement what is called the light-year, or the distance 
light would travel in one year. Since light moves through space with a velocity 
of about 186,000 miles a second, the enormous value of this unit will be readily 
Understood. It is equal to about 63,000 times the distance between the earth and 
the sun. Most of the stars that can be seen by the naked eye are probably situ- 
ated at distances of from 200 to 300 light-years. The distance of the remotest 
stars in the stellar system is unknown. It is believed, however, to be at least 
from 10,000 to 20,000 light-years. 

9. The Satellites. — A satellite is a body that revolves around 
another body : the planets are satellites of the sun ; the moon is a 
satellite of the earth. Mars has two moons or satellites. So far as 
now known, neither Mercury nor Venus has a satellite. All the 
planets whose orbits are beyond the orbit of the earth have moons : 



MATHEMATICAL GEOGRAPHY. 17 

Jupiter has five, Uranus four, Saturn nine, and Neptune one. 
Besides its moons, Saturn has a number of curious ring-like accu- 
mulations of separate solid or liquid particles revolving around it. 

10. The Earth's Moon. — The earth's moon is about 240,000 
miles from the earth. 




Fig. 2.— Full Moon. Taken from a photograph. 

Our moon always turns the same face toward the earth. Its 
opposite face is never visible to us. This is because the moon 
turns or rotates on its axis in the same time that it revolves in its 
orbit around the earth. 

The irregularities of light and shade seen in the face of the moon, as shown in 
Fig. 2, are due to irregularities in its surface. The moon has its highlands and 
2 



18 PHYSICAL GEOGRAPHY. 

lowlands, its mountains and its valleys. These mountains far surpass in height 
those of the earth. With telescopes of comparatively high magnifying power, 
these mountains are seen to be volcanoes, their craters in many instances being 
clearly discernible. 

An exceedingly careful study of the moon has failed to show any signs of the 
presence of either air or water on the surface that is turned toward us. 

11. The Sun is the great central body of the solar system. 
Around it move the planets with their satellites, receiving their 
light and heat from it. The sun is a huge heated mass about 
1,330,000 times the size of the earth. Its diameter is about 866,500 
miles. It appears the largest self-luminous body in the heavens 
because it is comparatively near the earth. Many stars, which 
appear as mere dots of light, are much larger than the sun. 

Were the sun hollow and the earth placed at its centre, there would not only 
be sufficient room to enable the moon to revolve at its present actual distance 
around the earth, but it would still, in all parts of its orbit, be nearly 200,000 
miles below the surface of the sun. 

Only a comparatively small portion of the sun is visible to us. The surface 
we ordinarily see is bounded by what is called the photosphere, a mass of lumi- 
nous clouds formed by the condensation of gaseous substances that exist lower 
down in the hotter body of the sun. 

Beyond the photosphere, resting on it, and partly penetrating it, is an enve- 
lope of permanent gases, mainly hydrogen and helium. This envelope is called 
the chromosphere. As seen during a total eclipse of the sun, the chromosphere 
resembles a scarlet sheet of flame, from which prominences or protuberances 
arise, often to the height of hundreds of thousands of miles. 

Above the chromosphere and resting on it, is another layer called the corona. 
This layer extends far beyond the distances to which the higher prominences 
of the chromosphere rise. The corona appears to consist of highly rarefied gaseous 
substances, together with some variety of meteoric dust or fog. The corona is 
visible only during eclipses of the sun at the time of totality. 

The sun is a body heated to luminosity, and gives out or emits light and heat 
like any other highly heated body. 

12. Position of the Solar System in Space. — The sun, with 
all the bodies which move around it, is in that portion of the heav- 
ens called the Milky Way. The sun is an insignificant star among 
the millions of other stars the telescope has revealed to us. 

It was formerly believed that the sun was stationary, for it was not then 
known that the positions of the fixed stars were undergoing slight variations 



MATHEMATICAL GEOGRAPHY. 



18a 



as regards the earth. It is now generally conceded that the sun, with all 
the planets, is moving through space with tremendous velocity, the direction 
at present being toward the constellation Hercules. The estimated velocity of 
the sun in its immense orbit is 1,382,000,000 miles per year. As the earth is 
carried along with the sim in its orbit, it is continually entering new realms of 
space. 

Phases of the Moon. — The different appearances of the moon changing 
every month from one shape into another are called its phases. If it shone with 
light of its own, it would always appear circular to us, as does the sun. These 




Fig. 2a.— The Moon's Phases. (The outer circle shows the moon as seen from the sun, 
the inner circle shows the moon as seen from our earth.) 

phases are due to two causes : first, to the fact that the moon is opaque ; second, 
to the fact that the earth's orbit and the moon's orbit are not in the same plane. 
The moon's orbit is inclined to the earth's at an angle of over 5°, so that the 
moon may be on the same side of the earth as the sun and not be on the straight 
line connecting them. Imagine the sun in the diagram to be shining through the 
book from a point several feet behind it and this fact will be more easily under- 
stood. 

Eclipses of the Moon and Sun. — The opaque earth throws out a long coni- 
cal shadow into space on the side away from the sun. When the moon is passing 



18b 



PHYSICAL GEOGRAPHY. 



through this shadow, it receives no light from the sun and is said to be in eclipse. 
These lunar eclipses would occur every month if the sun, moon, and earth were on 
a straight line, but the angle of inclination is 5°. They occur only at time of full 




Tig. 2b. 



-Relative Positions of the Moon, Earth, and Sun during an Eclipse 
of the Moon. 



moon, and according to the deviation of the earth, the sun, and the moon from a 
straight line, the moon may pass througli the centre of the shadow, or to one 
side of the centre, or merely dip into the light edge of it. When it passes through 
the dark middle and is entirely covered, we have a total eclipse. When only a 
small part of the moon is darkened, we have a partial eclipse. A total eclipse often 
lasts two hours and is visible from all parts of the earth then facing the moon. 




Fig. 2c.— Relative Positions of the Sun, Moon, and Earth during an Eclipse 

of the Sun. 



In an eclipse of the sun, the moon hides the sun from the earth. Here again, 
to have an eclipse the three bodies must be in a straight line drawn through 
their centres. However, an eclipse may occur even if the moon is not in an 



MATHEMATICAL GEOGRAPHY. 



19 



exact line with the sun and earth. The distance of the moon from the earth varies 
from 222,000 to about 253,000 miles. The moon is sometimes at her greatest dis- 
tance from the earth at the moment when she passes centrally over the sun, 
sometimes at her least distance, or at any intervening distance. If she is near 
the earth, lier surface just covers that of the sun and a total eclipse occurs. If she 
is at the greater distance, her disk seems smaller from the earth and a rim of the 
sun is left visible all around the moon. This is called an annular eclipse. The 
small moon's shadow is never larger than 165 miles in diameter. 



13. The Earth. — The shape of the earth is that of a round ball 
or sphere slightly flattened at two opposite sides. Such a body is 
termed a spheroid. There are two kinds of spheroids — oblate and 
prolate ; the former has the shape of an orange, the latter that of a 
lemon. 

The straight line that runs through the centre of a sphere or 
spheroid and terminates at its surface is called the diameter. 
If the sphere rotates — 
that is, spins like a top 
—the diameter on 
"vvhich it turns is called 
its axis. In the oblate 
spheroid the axis is the 
shorter diameter ; in 
the prolate spheroid the 
axis is the longer diam- 
eter. 

The shape of our 
earth is approximately that of an oblate-spheroid. The polar diam- 
eter is 26.47 miles shorter than the equatorial diameter. 

14. Proofs of the Rotundity of the Earth,— The earth is so 
large a sphere that its surface everywhere appears flat. The fol- 
lowing considerations will prove, however, that its form is nearly 
spherical : 

(1) Upper Parts of Vessels Seen Farthest.— If the earth were flat, as soon 
as an object appeared on the horizon we would see the upper and lower parts 
at the same time; but if it were curved, the top parts would first be seen. 
When a ship is coming into port we see first the funnels, then the superstructure. 




Fig. 3.— Oblate 
Spheroid. 



Fig. 4. — Prolate 
Spheroid, 



20 



PHYSICAL GEOGRAPHY. 




Fig. 5.— Steamers Entering Port. 



and finally the hull ; hence the earth must be curved ; and since the appearance 

is the same from whatever direction the ship is approaching, we infer that the 

earth is evenly curved or 
spherical. 

If the rigging of a dis- 
tant ship whose hull is 
below the horizon be ex- 
amined with a suitable 
telescope, it will at once 
be apparent that a consid- 
erable distance exists 
between the ship and the 
water line on the horizon, 
since, if the glass be 
sharply focused on the 
water line at tlie horizon, 
tlie sliip will become in- 
distinct, while, if the glass 
be sharply focused on the 
distant ship, the water 
line at the horizon will 
become indistinct. 
(2) The Earth's Shadow on the Moon. — We can obtain correct ideas 

of the shape of a body by the shape of the shadow it casts. The shadow 

which the earth casts on the moon 

during an eclipse of the moon is 

always circular, and as only spher- 
ical bodies cast circular shadows 

in all positions, we infer that the 

earth is spherical. 

(8) Increase of Horizon with 

Altitude. — An observer can see 

a wider stretch of land from the 

top of a hill than from its foot. 

The horizon seems both to enlarge 

and to sink as we ascend above 

the surface ; whereas, if the earth 

were flat our field of vision would 

not change, no matter how high 

we mounted. The horizon is al- 
ways circular, which would not 

be the case if the earth's form 

were not very nearly spherical. 

(4) Change of Constellations with Change of Latitude. — If an observer 




Fig. 6.— The Circular Shadow of the Earth 
Thrown on the Moon. 



MATHEMATICAL GEOGRAPHY. 21 

were to travel along a meridian from the equator to the poles, new constella- 
tions would constantly become visible. These would previously be hidden by 
the earth's curvature. 

(5) Variation of Time vfith Longitude — Since the earth turns through 
360° in about 24 hours, it turns eastward 15° in every 60 minutes. Conse- 
quently, if the sun is just rising on a certain meridian, it is one hour before 
sunrise on the meridian 15° to the west. This would not be the case if the 
earth were flat. 

(6) Weiglit of a Body increases with Latitude. — When in high latitudes, 
a body weighs slightly more than in low latitudes. This means that it is nearer 
the centre of the earth in the high latitudes than in the low; or, in other 
words, that the earth is not a true sphere. 

Consequences of the Earth's Shape. — Gravity — The spheroidal shape of 
the earth greatly facilitates transportation over its surface. This in turn makes 
world commerce possible. Again, the earth exerts an attraction on all bodies 
upon it that we call gravity. By this force men are held to the earth's surface, 
the air is prevented from flying off into space, and the oceans are held in place. 
Gravity gives to the ocean a curved surface, but it aids commerce in another 
important way. Its downward pull causes bodies to have weight. Because 
the earth is nearly round, gravity is nearly equal everywhere upon its sur- 
face, and, as we have already seen, the weight of a given object is therefore 
nearly constant. If the weight of things varied greatly from place to place, 
this variation would interfere seriously with trade between different parts of 
the world. 

15. The Dimensions of the Earth. — The equatorial diameter 
of the earth, or the shortest distance through at the equator, is, 
approximately, 7926 miles ; its polar diameter, or the length of its 
axis, is 7899 miles. The equatorial circumference is 24,899 miles. 
The entire surface is equal to nearly 197,000,000 square miles. 

The density of the earth is about 5| ; that is, excluding the atmosphere, the 
total weight of all its matter is five and two-thirds times greater than an equal 
volume of water. 

16. Imaginary Circles. — In order to locate places on the earth, 
as well as to represent portions of its surface on maps, we imagine 
the earth to be encircled by a number of curved lines called great and 
small circles. 

A great circle is one which would be formed on the earth's sur- 
face by a knife or plane passing through the earth's centre, hence 
dividing it into two equal parts. All great circles, therefore, divide 
the earth into hemispheres. 



22 PHYSICAL GEOQBAPHY. 

The formation of a great circle on a sphere by cutting it into two equal parts 
is shown in Fig. 7. 

The shortest distance between any two places on the earth is along the arc of 
a great circle. 

All planes passing through the earth's centre form, approximately, great cir- 
cles on its surface. 

A small circle is one formed by a plane which does not cut the 
earth into two equal parts. 

The formation of a small circle by cutting a sphere into unequal parts is shown 
in Fig. 8. 

The great circles employed most frequently in geography are the 
equator and the meridian circles. The small circles are the parallels'^ 



im^ 



1 /X 

i ii 







Fig. 7.— Great Circle. Fig. 8.— Small Circle. 

If we divide the circumference of anj' circle, whether great or small, into 
three hundred and sixty equal parts, each part is called a degree. The one- 
sixtieth part of a degree is a minute ; one-sixtieth part of a minute is a second. 
The characters representing these divisions are used as follows: 34°, 12', 38"; 
which indicates thirty-four degrees, twelve minutes, and thirty-eight seconds. 

The Equator is that great circle of the earth which is equidis- 
tant from the poles. 

Meridian Circles are great circles of the earth which pass 
through both poles. 

The Meridian of any given place is that half of the meridian 
circle which passes through that place and both poles. A meridian 
of any place reaches from that place to both poles, and therefore is 
equal to one-half of a great circle, and, with the meridian directly 



MATHEMATICAL GEOGRAPHY. 23 

opposite to it, forms a great circle called a meridian circle. There 
are as many meridian circles as there are places on the equator or 
on any parallel. 

In large cities the meridian is g:enerally assumed to pass througli the principal 
observatory. 




Fig. 9.— Meridians and Parallels. 

Parallels are small circles which pass around the earth parallel 
to the equator. 

The meridians extend due north and south, and are everywhere of the same 
length; the parallels extend due east and west, and decrease in length as they 
approach the poles. 

The Tropics are parallels which lie 23° 27' north and south of 
the equator : the northern tropic is called the Tropic of Cancer, the 
southern tropic is called the Tropic of Capricorn. 

The Polar Circles are parallels which lie 23° 27' from each pole. 
The polar circle in the Northern HemisjDhere is called the Arctic 
Circle; that in the Southern Hemisphere, the Antarctic Circle. 

17. Latitude is distance north or south from the equator toward 
the poles, measured along the meridians. It is reckoned in degrees. 

The meridian circles are divided into nearly equal parts by the parallels, and 
it is the number of these parts that occur on the meridian of any place between 
it and the equator, which determines the value of its latitude. If we conceive 
eighty-nine equidistant parL.'lels drawn between the equator and either pole, 
they will divide all the meridians into ninety nearly equal parts ; the value of 
each of these parts will be one degree of latitude. Therefore, if the parallel run- 
ning through a place is distant from the equator forty-five of these par^s, ita 



24 PHYSICAL GEOGRAPHY. 

latitude is 45°. If more than eighty-nine parallels be drawn, the value of each 
part will be less than one degree. 

Places north of the equator are in north latitude ; those south of 
it are in south latitude. Places near the poles are said to be in 
high latitudes; those near the equator, in low latitudes. 

Since the distance from the equator to the poles is one-fourth of 
an entire circle, and there are only 360° in any circle, 90° is the 
greatest value of latitude a place can have. Latitude 90° N., there- 
fore, corresponds to the north pole. 

To recapitulate : Latitude is measured on the meridians by the 
parallels. 

18. Longitude is distance east or west of any given meridian. 

Places on the equator have their longitude measured along it ; everywhere 
else longitude is measured along the parallels. 

The meridian from which longitude is reckoned is called the 
Prime Meridian. Most nations take the meridians of their own 
capitals for their prime meridian. The English reckon from the 
meridian which runs through the observatory at Greenwich, and 
this is the meridian used for all calculations at sea. In the United 
States we reckon, in land surveys, from Washington. A place situ- 
ated east of the prime meridian, is in east longitude ; west of it, is 
in west longitude. 

Since there are only 180° in half a circle, the greatest value the longitude can 
have is 180° ; for a place 181° east of any meridian would not fall within the 
eastern half of the parallel on which it is situated, but in the western half; and 
its distance, computed from the prime meridian, would be 179° west. 

It is the meridians that divide the parallels into degrees ; there- 
fore, longitiide is measured on the parallels by the meridians. 

19. Value of Degrees of Latitude and Longitude. — As 
latitude is distance measured on the arc of a meridian, the value 
of one degree must be the -g-g-oth part of the circumference along 
that meridian, since there are only 360° in all. This makes the 
value of a single degree, approximately, equal to 69} miles. Near 
the poles the flattening of the earth causes the value of a degree 
slightly to exceed that of one near the equator. 



MATHEMATICAL GEOGRAPHY. 25 

Length of 1° Latitude at Different Distances from the Equator. 

Latitude 0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 

Length in miles . . . 68.70 68.72 68.78 68.83 68.98 69.11 69.22 69.31 69.36 69.39. 

The value of a degree of longitude is subject to great variation. 
It is equal to the y^th part of the earth's circumference, provided 
the place be situated on the equator ; otherwise, it is the gxoth part 
of the parallel passing through the place whose longitude is taken ; 
and as the parallels decrease in size as we approach the poles, the 
value of a degree of longitude must likewise decrease as the latitude 
increases, until at either pole the longitude becomes equal to zero. 

The value of a single degree of longitude on the equator, or at latitude 0°, is 
equal to about 69^ miles. 

At latitude 45° it is equal to about 49 miles. 
60° " " 35 " 

" 80° " " 12 " 

90° " " " 

Geographical Mile. — The sri^njth of the equatorial circumference, or the 
one-sixtieth of a degree of longitude at the equator, is called a nautical or geo- 
graphical mile. The statute mile contains 1760 yards ; the geographical or 
nautical mile, 2028 yards. The nautical mile is sometimes called a knot. 

20. Map Projections. — The term projection as applied to map- 
drawing means the method used for representing portions of the 
earth's surface on the plane of a sheet of paper. 

The projections in most common use are Mercator's, the stereo- 
graphic, and the conical projections. Of these the stereographic is 
best adapted to ordinary geographical maps where not more than one 
hemisphere is to be represented, and Mercator's to physical maps. 
All projections must be regarded as but approximations. 

Mercator's Projection represents the earth on a map in which 
all the parallels and meridians are straight lines. 

Mercator's charts are drawn by conceiving the earth to have the 
shape of a cylinder instead of that of a sphere, and to be unrolled 
from this cylinder so as to form a flat surface. The meridians, 
instead of meeting in points at the north and south poles, are drawn 
parallel to each other. This makes them as far apart in the polar 
regions as at the equator, and, consequently, any portion of the earth's 



26 



PHYSICAL GEOGRAPHY. 



surface represented ou such a chart, if situated near the poles, will 
appear disproportionally large. In order to avoid the distortion in the 
shape of the land and water areas, the distance between successive 
parallels is increased as they approach the poles. The dimensions 
of the land or water, however, are made to appear much larger than 
they really are in the polar regions ; for example, Greenland is made 



*^ 7 


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i 




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m 


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W 






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Fig. 10.— Ttie Earth on Mercator's Projection. 

to appear nearly as large as Africa. The immediate polar regions 
are never represented on such charts, the poles being supposed to be 
at an infinite distance. 

Mercator's charts are usually employed for physical maps, on account of the 
facility they aiford for showing direction. 

Gall's Projection is a Tariety of Mercator's projection in which the paral- 
lels are more nearly equidistant from, each other, thus destroying their facility 
for showing direction correctly, but giving less distortion of areas in high 
latitudes. 

The Orthographic Projection is a picture of a globe as it appears from a 
distance many times its diameter. Straight parallel lines, extended from the 
meridians and parallels of tlie globe upon a plane surface perpendicular to tiiem, 
locate the network of the map. The areas are correct near the centre, but around 
the edges they are greatly reduced. 

The Stereographic Projection is a picture of a transparent hemisphere as it 
would appear to an observer whose eye was placed at the middle point of the 
surface of the opposite hemisphere. In this map the areas are reduced near the 
centre and enlarged towards the edges. Two common stereographic projections 
are the Equatorial and the Polar. In an Equatorial Projection the equator 
passes through the middle of each hemisphere, and a meridian circle forms the 



MATHEMATICAL GEOGRAPHY. 



27 



borders. In a Polar Projection the poles occupy the centres of each hemi- 
sphere, and the equator forms the borders. 

In a Conical Projection the surface represented is conceived to be that of a 
cone cut lengthwise and flattened out. The parallels are arcs of equidistant, con- 




Fig. 11.— Orthographic Projection. Fig. 12.— Stereographic Projection. 

centric circles, and the meridians are radiating straight lines intersecting the 
parallels at right angles. For areas of no great extent in latitude, such as the 
United States, a map on this projection is_ very nearly correct. 

Variation in Map Scales. — The scale to which a map is drawn is the ratio 





Fig. 13.— The Same Topography Eepresented on the Left by a Model, on the 
Eight by Contour. 

which distances and areas on the map bear to the actual distances and areas on 
the earth. Scales are expressed by ratios, as 1 : 100,000, which means that one 
inch on the map corresponds to one hundred thousand inches on the earth; or in 
linear units, as 1 inch = 10 miles ; or by graduated lines. For small areas the 



28 PHYSICAL GEOGRAPHY. 

scale may be large, one foot or more to the mile ; for large areas it must be small. 
On maps of large areas no uniform scale can apply exactly to all parts. 

Contour, Hachure, and Relief Maps. — The surface of the land is uneven, 
and it is a matter of importance to show the unevenness on maps. This is done 
in several ways. A wide use is made of hachures to represent the irregularities of 
the surface of small sections. A hachure map is one in which the relief is 
brought out by shading, through the use of lines drawn more or less closely to- 
gether, and all pointing in the direction of the slope. An example is shown in 
the map on page 364. 

Contour-line maps give more exact information. Contours are lines drawn on 
maps to express relief, and any given line runs through all points of the same 
elevation above sea level. Every place through which the 100-foot contour 
passes is just 100 feet above sea level. On such maps, therefore, it is possible 
to tell the elevation of every place. The vertical distance between two adjacent 
contour lines is the contour interval. 

Sometimes varied colors are used to show the general distribution of highlands 
and lowlands. An example is found in the map on pages 332-333. A far better 
means of representing a country is by relief map in which the surface is actually 
raised. 

21. The Hemispheres. — The equator divides the earth into a 

Northern and a Southern Hemisphere. 

The meridian of long. 20° W, from Greenwich is usually taken 
as the dividing-line between the Eastern and Western Hemispheres. 

22. The Movements of the Earth; Rotation. — The earth 
turns around from west to east on its diameter or axis. This motion 
is called its rotation. 

To a person in a rapidly moving steam-car, the fences and other objects along 
the road will appear to be moving in the opposite direction : their motion is of 
course apparent, and is caused by the real motion of the car. Now, the motion 
of the sun and the other heavenly bodies, by which they appear to rise in the 
east and set in the west, is apparent, and is caused by the real motion of the 
earth on its axis ; this motion must therefore be from west to east. The sun, the 
planets, and their satellites, so far as is known, also turn on their axes from west 
to east. 

The earth makes one complete rotation in about every twenty-four 
hours — accurately, 23 hours, 56 minutes, 4.09 seconds. The velocity 
of its rotation is such that any point on the equator will travel about 
1042 miles every hour. The velocity, of course, diminishes at points 
distant from the equator, until at the poles it becomes nothing. 

23. Proofs of the Rotation of the Earth.— That it is the 



MATHEMATICAL GEOGRAPHY. 



29 



earth that is rotating, or moving under the heavens, and not the 
heavens moving over the earth may be adduced as follows : 

(1) Prom Analogy. — By the use of the telescope we can see 
that the sun, moon, and pianets are actually rotating or turning on 
their axes ; hence it is probable that the earth also is rotating. 

(2) Poucault's Pendulum. — In 1851, Foucault suspended a 
heavy iron ball from the dome of the Pantheon, in Paris, by a wire 
about 200 feet long, as shown 

in Fig. 14. The ball had, ' 
attached to its lower extrem- 
ity, a pin so placed as to just 
cut or scrape a ridge of sand 
placed on a circular platform 
on the floor below it. On 
starting the pendulum to swing 
in a true plane, by drawing the 
ball aside by a cotton thread, 
letting it come absolutely to 
rest, and then burning the 
thread, it was found that the 
floor seemed to move to the 
right, the ball cutting the 
ridge of sand at each vibra- 
tion in a different place ; or, in other words, the floor of the Pan- 
theon was visibly moving or turning under the plane in which the 
pendulum was vibrating. 

(3) Bodies falling from a great height are slightly deflected 
toward the east. Projectiles show a similar deviation. 

(4) The deviation of the winds and ocean currents, and the rota- 
tion of the wind in cyclones, demonstrate the rotation of the earth 
from west to east. 

24. Change of Day and Nig-ht. — The earth receives its light 
and heat from the sun, and, being an opaque sphere, only one-half 
of its surface can be lighted at one time. The other half is in dark- 
ness, since it is turned from the sun toward portions of space where 




Fig. 14. 



-Foucault' s Pendulum Experi- 
ment. 



30 PHYSICAL GEOGRAPHY. 

it receives only the dim light of the fixed stars. The boundary-line, 
between the light and dark parts, forms, approximately, a great circle 
called the Great Circle of Illumination. Had the earth no motion 
either on its axis or in its orbit, that part of its surface turned 
toward the sun would have perpetual day, and the other part per- 
petual night ; but by rotation, different portions of the surface are 
turned successively toward and away from the sun, and thus is occa- 
sioned the change of day and night. 

Effects on Habits of Life. — Human activities are in general adjusted to 
the turning of the earth, the succession of light and darkness affording convenient 
intervals for work and rest. In daylight, plants and animals, including man, are 
active in obtaining food. Darkness is a period of rest during which they assimi- 
late food, build up tissue, repair waste, and renew strength. For men the reg- 
ular and frequent recurrence of periods of sleep, preferably during the hours of 
darkness, is absolutely necessary to health and efficiency. 

The period of rotation furnishes also a natural unit for measuring time. 
Again, the rising and setting of the sun, due to the earth's rotation, gives us a 
simple system of directions. 

25. The Revolution of the Earth.- — The earth has also a 
motion around the sun, called its revolution. 

The revolution of the earth is from west to east; this is true also 
of all the planets and asteroids, and of all their satellites, except 
those of Uranus, and, probably, of Neptune. 

The earth makes a complete revolution in 365 days, 6 hours, 9 
minutes, 9.6 seconds. This time forms what is called a sidereal year. 
The tropical year, or the time from one March equinox to the next, 
is somewhat shorter, or 365 days, 5 hours, 48 minutes, 49.7 seconds. 
The latter value is the one usually given for the length of the 
year. It is nearly 3651 days. 

It will be found that the sum of the days in all the months of an ordinary 
year is only equal to 365, while the true length is, approximately, one-quarter of 
a day greater. This deficiency, which in every four years amounts to an entire 
day, is met by adding one day to February in every fourth or leap year. The 
exact time of one revolution, however, is about 11 minutes less than 6 hours. 
These eleven extra minutes are taken from the future, and are paid by omitting 
leap year every hundredth year, except that every 400 years leap year is counted. 
In other words, 1900 was not a leap year, since 1900 is not exactly divisible by 
400, but the year 2000 will be a leap year. 



MATHEMATICAL GEOGRAPHY. 



30a 



The length of the orbit of the earth is about 577,000,000 miles. 
Its shape is that of an ellipse which differs but little from a circle. 
The sun is located at one focus of the ellipse, and, as this is not in 
the centre of the orbit, the earth must be nearer the sun at some 
parts of its revolution than at others. 



rerilielion 




ApUelioa 



Fig. 14a. 

When the earth is in that part of its orbit which is nearest to the sun, it is 
t;aid to be at its perihelion ; when in that part farthest from the sun, at its aphe- 
lion. The perihelion distance is about 90,259,000 miles ; the aphelion distance, 
93,750,000 miles. The earth reaches its perihelion about January 1st. 

The earth does not move with the same rapidity through all parts of its orbit^ 
but travels more rapidly in perihelion than in aphelion. Its mean velocity is 
nearly 90 miles a second, which is about sixty times faster than the speed of a 
cannon-ball. 

The actual motion of the earth through space during its revolutions around 
the sun is proved by the annual parallax of the fixed stars, whereby each fixed 
star appears every year to be moving through the sky as if it were moving in a 
little orbit of 186,000,000 miles, the counterpart of the earth's orbit. This can 
only be explained by the actual motion of the earth in its orbit around the sun. 

Measurement of Time. — The rotation and revolution of the earth furnish 
1;wo units for measuring time, the day and the year. The period from the mo- 
ment when the sun reaches his highest point in the heavens and is on the me- 
ridian, to the moment when he next reaches the same point, varies from day to 
day. The average length of this solar day is divided into the hours, minutes, and 
jreconds shown by ordinary clocks and watches. The civil day, for convenience, 
is made to begin and end at midnight, and is of the same length in every part of 
the world. Inside the polar circles the civil day does not always correspond to 
Sictual day and night, since the time from sunrise to sunset varies from a few 
minutes to six months. 

Longitude and Time. — There is a definite relation between longitude and 
Vime. Since the earth turns through 360° in 24 hours, it turns 15° in one hour. 



30b 



PHYSICAL GEOGRAPHY. 



or 15' of longitude in one minute of time. Tlie sun therefore rises one hour 
earlier at a place in longitude 0° than in a place in the same latitude in lon- 
gitude 15° W., and one hour later than at a place in the same latitude in longi- 
tude 15° E. All places on a given meridian have noon and midnight at the same 
time, and such places are said to have the same solar time ; but places on different 
meridians have different times. 

If longitude may be used to determine time, it is evident that time may be 
used to determine longitude. Ships are able in this way to determine their posi- 
tion. They start with an accurate chronometer, set to Greenwich time. By 




Fig. 14b. 

means of a sextant, an officer observes the sun to determine the local noon, that 
is, the time when the sun has reached its highest position. Comparing this local 
time with that of the chronometer, it is easy to tell the difference between 
Greenwich time and that where the ship is. Since one hour's difference means 
15° of longitude, the longitude of the ship is determined. 

Standard Time. — Local mean solar time is most convenient for people resid- 
ing in one place, but for travellers and railroad companies some other method of 
measuring time is required. A watch adjusted in New York has not the correct 
time when carried to Chicago. To avoid the difficulties of time-keeping growing 
out of travel, the railroads of the United States and Canada have adopted a sys- 
tem of standard time. The country is divided into north-south belts, about 15° 
wide, and all places in each belt use the same time. The railway time in adjacent 



MATHEMATICAL GEOGRAPHY. 31 

telts differs by one hour. By this system the clocks and watches do not show 
correct local or solar time except on one meridian of each belt. In Xorth America 
five standard time belts are in use as shown in the diagram. The boundaries of 
these belts are irregular. Wlien a traveller crosses the boundary of a time belt 
he sets his watch forward, or back, one hour. Nearly all civilized countries have 
adopted standard time meridians. 

International Date Line.^If one travels westward, solar time becomes 
slower at the rate of one hour for every 15° of longitude. In going around the 
earth a watch must be set back in all 24 hours, which would cause the traveller 
to lose one day from his calendar. In travelling eastward he adds a day. Hence 
it is found necessary to fix upon an arbitrary line for the correction of the calen- 
dar. This is called the International Date Line, and for all vessels is the meridian 
of 180°. When a ship crosses this to the westward, a day is added to the reck- 
oning, but if to the eastward, a day is dropped. The Conventional or International 
Day begins immediately after the stroke of midnight in London. The sun is 
then passing the meridian of 180°, and it is noon on this hne. Tor example, 
when the midnight of December 31 has arrived in London, immediately January 
1 has begun there. On the International Date Line we know that it is the noon 
of December 31 until the sun reaches the 180° meridian. Immediately upon the 
sun's passing that meridian, it is the noon of January 1 at the edge of the 
eastern hemisphere. 

26. Laplace's Nebular Hypothesis. — The uniformity in the 
direction of rotation and revolution of the planets has led to a very 
plausible supposition as to the origin of the solar system, by the 
celebrated French astronomer, Laplace. This supposition, known 
as Laplace^s Nebular Hypothesis, assumes : 

(1) That at some very remote time the sun, together with all its planets and 
their satellites, was collected in a single nebulous or cloud-like mass of intensely 
heated gas. 

(2) That this mass gradually collected under its own gravitation into an 
approximately globular mass, and began rotating. 

(3) On gradually cooling, the central mass or sun contracted, and, consequently, 
rotated more and more rapidly, flattening at the poles and bulging out at the 
equator, finally detaching a ring of nebulous matter, as in Saturn's rings. 

(4) That this ring would revolve around the central sun, and, subsequently; 
break and collect in a globular mass that would revolve around the central sun 
as a planet. These rings and planets would be successively thrown off from the 
central mass as it contracted, the planets similarly throwing off moons or satel- 
lites. 

The nebular hypothesis is not generally credited in all its details. Though 
probably true in the main, it appears to need modification. For example, l/ock- 
yer insists that the original central mass, instead of being formed of glowing gas, 
consisted of a cloud of ice-cold meteoric dust. 




32 PHYSICAL QEOGRAPHT. 

27. The Plane of the Earth's Orbit is a perfectly flat surface 

that touches the earth's orbit at every point. It may be regarded as 

an imaginary plane of enormous extent on 

which the earth moves in its journey around 

the sun. 

28. Causes of the Change of Sea- 
sons. — The change of the earth's seasons 
is caused by the revolution of the earth, 
together with the following circumstances : 

(1) The inclination of the earth's 

axis to the plane of its orbit. The incli- 
Fig. 15.— Inclination of ... i , aao oq/ 

. - * « T,i. ^ T, T nation is equal to bo 66 . 
Axis to Orbit and Eclip- ^ 

tic. The ecliptic is the name given to a great circLj 

whose plane coincides with the plane of the earth'ij 
orhit. Since the earth's axis is 90° distant from the equator, the plane of th« 
ecliptic must be inclined to the plane of the equator 90° minus 66° 33', or 23° 27',. 
The mere revolution of the earth would be unable to produce a change of 
seasons, unless the earth's axis were inclined to the plane of its orbit. If, foi ■ 
example, the axis of the earth stood perpendicularly on the plane of its orbit, 
the sun's rays would so illumine the earth that the great circle of illumination 
would always be bounded by some meridian circle. The days and nights would 
then be of equal length, and the distribution of heat the same throughout the 
year. Under these circumstances there could be no change of seasons, because 
the sun's rays would always fall perpendicularly on the same part of the earth : 
t. e., on the equator. 

(2) The Constant Parallelism of the Earth's Axis. — During 
the earth's revolution its axis always points nearly to the same place 
in the heavens ; viz., to the north star. It is. therefore, always ap- 
proximately parallel to any former position. 

Unless the axis were constantly parallel to any former position, the present 
change of seasons would not occur. 

On account of the spheroidal form of the earth, only a small part 
of its surface can receive the vertical rays of the sun at the same 
time. This part may be regarded as nearly a point ; and since only 
one-half of the earth is lighted at any one time, the great circle of 
illumination must extend 90° in all directions from the point which 
receives the vertical rays. By rotation, all portions of the surface 



MATHEMATICAL GEOGRAPHY. 



33 





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situated anywhere •within the tropics in the same latitude are 
at some time during the day, so turned as to receive the verti- 
cal rays of the sun, and, consequently, the portion so illumined 
has the form of a ring 
or zone. Other things 
being equal, this zone 
contains the hottest por- 
tions of the surface, the 
beat gradually dimin- 
ishing as we pass toward 
either pole. 

On account of the 
inclination of its axis, 
the earth receives the 
vertical rays of the sun 
on new portions of its 
surface every day dur- 
ing its revolution ; and 
it is because different 
portions of the earth's 

surface are constantly being turned toward the sun that the change of 
seasons is to be attribxded. 

As the earth changes its position in its orbit, the sun's rays fall 
vertically on different parts of the surface, so that during the year 
some part of the surface within 23° 27^ on either side of the equator, 
receives the vertical rays. 

The astronomical year begins on the 20th of March, and we shall, therefore, 
first consider the position of the earth in its orbit at that time. 

An inspection of Fig. 16, will show that at this time the earth is so turned 
toward the sun that the vertical rays fall exactly on the equator. The great circle 
of illumination, therefore, reaches to the poles, and the days and nights are of 
an equal length all over the earth. This time is called the March equinox_ 
Spring then begins in the Northern Hemisphere, and autumn in the Southern. This 
is shown more clearly in Fig. 17, which represents the relative positions of the 
illumined and non-illumined portions at that time. 

As the earth proceeds in its orbit, the inclination of the axis causes it to turn 
the Korthern Hemisphere more and more toward the sun. The vertical rays, 



Fig. 16.— The Orbit of the Earth, showing the 
Change of Seasons. 



34 



PHYSICAL GEOGRAPHY. 



therefore, fall on portions farther and farther north until, on the Slst of Jtme, the 
vertical rays reach their farthest northern limit, and fall directly on the Tropic of 
Cancer, 23° 27' N., when the sun is said to be at its summer solstice. 

Since the portions receiving the vertical rays of the sun are now on the Tropic 
of Cancer, the light and heat must extend in the Northern Hemisphere to 23° 
27' beyond the north pole, or to the Arctic Circle ; while in the Southern Hemi- 
sphere they must fall short of the south pole by the same number of degrees, or 
reach to the Antarctic Circle. The Northern Hemisphere then begins its summer, 
and the Southern, its winter. 

The relative positions of the illumined and non-illumined portions of the 
earth at the summer solstice are more clearly shown in Fig. 18. Here, as is 
shown, the great circle of illumination extends in the Northern Hemisphere as 
far over the pole as the Arctic Circle. 

After the 21st of June the Northern Hemisphere is turned less toward the 
sun, and the vertical rays continually approach the equator, all the movements of 





Fig. 17.— The Earth at an Equinox. 



Fig. 18. 



The Earth at the Summer 
Solstice. 



the preceding season being reversed, until on the 2Sd of September, the time of the 
September equinox, the equator again receives the vertical rays, the great circle of 
illumination again coinciding with the meridian circles. The earth has now 
moved from one equinox to another, and has traversed one-half of its orbit, 
and the Southern Hemisphere begins its spring, and the Northern, its autumn. 

From the 22d of September until the 20th of March, while the earth moves 
through the other half of its orbit, the same phenomena occur in the Southern 
Hemisphere that have already been noticed in the Northern. Immediately 
after the 22d of September the inclination of the axis causes the earth to be so 
turned toward the sun that its rays begin to fall south of the equator ; and, as 
the earth proceeds in its orbit, the Southern Hemisphere is turned more and 
more toward the sun, and the vertical rays fall farther and farther toward the 



MATHEMATICAL GEOGRAPHY. 



35 



pole. This continues until the Slst of December, when the rays fall vertically on 
the Tropic of Capricorn, and the December solstice is reached. The great circle of 
illumination now extends beyond the south pole as far as the Antarctic Circle, 
but falls short of the north pole 23° 27', reaching only the Arctic Circle. Summer 
then commences in the Southern Hemisphere, and winter in the Northern. 

After the 21st of December the Southern Hemisphere is turned less and less 
toward the sun, and the part receiving the vertical rays approaches the equator, 
until on the 20th of March the equator again receives the vertical rays, and, 
with the March equinox, spring commences in the Northern Hemisphere, and 
with it a new astronomical year. 

The equinoxes and solstices, as a rule, occur on the dates named. Occasionally 
they occur a short time before or after said dates. 

29. Mathematical Zones.— The Torrid Zone.— That belt of 
the earth's surface which lies between 
the tropics is called the Torrid Zone. 
At some time during the year every 
part of its surface receives the vertical 
rays of the sun. 

The Temperate Zones are included 
between the tropics and the polar cir- 
cles. The northern zone is called the 
North Temperate Zone, and the southern 
zone, the South Temperate Zone. 

The Polar Zones are included be- 
tween the polar circles and the poles. 
The northern zone is called the North 
Frigid Zone, and the southern zone, the Soiith Frigid Zone. 

These zones, which are separated by the parallels of latitude, are usually 
termed the astronomical or mathematical zones to distinguish them from others 
called physical zones, which are bounded by the lines of mean annual temper- 
ature. 

It will be noticed that both the distance of the tropics from the equator, and 
of the polar circles from the poles, is 23° 27', or the value of the inclination of 
the plane of the ecliptic to the plane of the equator. 

Apart from other causes, the winter in the Northern Hemisphere, outside the 
tropics, is less severe than at corresponding latitudes in the Southern Hemisphere, 
not only because the earth is nearest the sun during midwinter in the Northern 
Hemisphere, but also because the earth moves more rapidly when in perihelion 
than in aphelion. Consequently, the contrast of the seasons, so far as these causes 




Fig. 



19. — Mathematical Cli- 
matic Zones. 



36 PHYSICAL GEOGRAPHY. 

are concerned, is greater in the Southern than in the Northern Hemisphere. As 
we shall hereafter see, this eflFect is to some extent modified by the greater quan- 
tity of water in the Southern Hemisphere. 

30. Length of Day and Night. — Whenever more than half of 
either the Northern or the Southern Hemisphere is illumined, the 
great circle of illumination will divide the parallels unequally, and 
the length of the daylight in that hemisphere will exceed that of the 
night in proportion as the length of the illumined part, measured 
along any of the parallels, exceeds that of the non-illumined part. 

The length of daylight or darkness may exceed that of one com- 
plete rotation of the earth. The great circle of illumination may 
at times pass over either pole as far beyond as 23° 27' ; so that 
places situated within this limit may remain during many rotations 
exposed to the rays of the sun. 

The longest duration of daylight must occur at the poles, since the poles must 
continue to receive the sun's rays from the time they are first illumined at one 
equinox until the sun passes through a solstice and returns to the other equinox. 
Nowhere, outside the polar circles, will the length of daylight exceed one entire 
rotation of the earth. 

The length of the longest day at the equator, latitude 0°, is 12 hours. The 
length of the longest day at the poles, latitude 90°, is six months. 

»oj«ioo 

SYLLABUS. 

There are three kinds of Geography : Mathematical, Political, and Physical. 
Commercial Geography is sometimes added to these. 

Physical Geography treats of land, water, air, plants, animals, and minerals. 

Geography deals mainly with the earth's present condition ; Geology deals 
with the earth's condition both in the past and present. 

The earth continues its motion around the sun in consequence of its inertia. 

Some of the distant stars are highly heated, and shine by their own light ; 
others are dark, being too cold to emit light. 

The solar system constitutes the sun and the bodies that revolve around it. 
The sun is about 1,330,000 times larger than the earth. The sun is a body heated 
to luminosity, and gives out or emits light and heat, like any other heated body. 
The surface of the sun that we ordinarily see is bounded by the photosphere. 
Beyond, and resting on the photosphere, is a gaseous envelope called the chromO' 
tphere. Above this is a highly tenuous layer called the corona. 



SYLLABUS. 37 

The shape of the earth is that of an oblate spheroid whose equatorial diameter 
is about 26 miles longer than its polar diameter. 

That the earth is round and not flat is proved : (1) By the appearance of 
approaching or receding bodies; (2; By the circular shape of the horizon; (3) 
By the shape of the earth's shadow; (4) By actual measurement; (5) By the 
shape of the great circle of illumination. 

The earth's diameter is nearly 8000 miles, its circumference not quite 25,000 
miles, and its area about 197,000,000 square miles. 

The imaginary circles employed in geography are the equator, the meridian 
circles, and the parallels. 

Latitude is measured on the meridians by the parallels. The greatest value 
the latitude of a place can have is 90° ; the greatest value of longitude is 180°. 

Longitude is measured on the equator or on the parallels by the meridians. 

Maps are drawn on different projections. Mercator's, Gall's, and the Equa- 
torial and Polar projections are those in most general use. 

That the earth rotates on its axis from west to east is proved : (1) By Fou- 
cault's pendulum ; (2) By falling bodies ; and (3) By the deviation of the winds 
and the ocean-currents. It is rendered probable by analogy. 

In all maps north and south lie along the meridians, east and west along the 
parallels ; when these are curved lines, the top and bottom of the map do not 
always represent north and south, nor the right and left, east and west. 

The change of seasons is caused by the inclination of the earth's axis to the 
plane of its orbit, and the constant parallelism of the axis to any former position 
when taken in connection with its revolution round the sun. 

The astronomical year begins March 20th. The equinoxes occur on the 20th 
of March and the 22d of September ; the solstices on the 21st of June and the 
21st of December. 

The Torrid Zone is the hottest part of the earth because at some time during 
the year every part of its surface receives the vertical rays of the sun. 



REVIEW QUESTIONS. 

The Solar System. 

How does the principle of inertia apply to the earth's motion around the sun ? 
What do you understand by the solar system ? 

Describe the earth's position in the solar system. Which of the planets are 
between the earth and the sun ? Which are beyond the orbit of the earth? 
What is a satellite ? Which of the planets have satellites ? 
How does the size of the sun compare with that of the earth ? 
Are any of the distant stars larger than our sun? 
Distinguish between the sun's photosphere, chromosphere, and corona. 



38 PHYSICAL GEOGRAPHY. 

In what part of space is the solar system ? 
Has our sun any motion through space? 
Enumerate the proofs of the rotundity of the earth. 

State accurately the length of the equatorial diameter of the earth; of its 
polar diameter; of its circumference. What is its area? 

How many times heavier is the earth than an equally large globe of water? 

Imaginary Circles. 

Define great and small circles. Name the circles most commonly used in 
geography. 

What do you understand by latitude? How is latitude reckoned? Of what 
use is latitude in geography ? Why can the value of the latitude never exceed 
90°? Of what use are meridians and parallels in measuring latitude? 

What do you understand by longitude? How is longitude reckoned? Of 
what use is longitude in geography? Why can its value never exceed 180°? 
Of what use are meridians and parallels in measuring longitude? 

Where is the value of a degree of latitude the greatest? Of a degree of Ion 
gitude? Why? 

What eiTect has a Mercator's chart on the appearance of bodies of land or 
water in high northern or southern latitudes? 

How does Gall's projection differ from Mercator's projection? 

What is an equatorial projection? A polar projection? A conical projection? 
What is the position of the poles in an equatorial projection of a hemisphere? 
In a polar projection? 

Movements of the Earth. 

Prove that the earth turns on its axis from west to east. 

Explain the cause of the change of day and night. 

Define a sidereal year; a tropical year. Which value is generally taken for 
the length of the civil year? 

Describe Laplace's nebular hypothesis. 

Enumerate the causes which produce the change of seasons. 

On what days of the year will the sun's rays fall vertically on the equator f 
On the Tropic of Cancer? On the Tropic of Capricorn? 




Fig. 19a.— St. Thomas, an Island of the "West Indies Resting on the Continental 
Shelf of North and South America. 



PART II. 
THE LAND. 



=>J«{o 



Although water occupies the larger portion of the earth's sur- 
face, yet, when compared with the entire volume of the earth, its 
quantity is comparatively insignificant ; for the mean depth of 
the ocean probably does not exceed two and one-third miles, and 
underneath this lies the cooled solid crust, with its heated interior. 

The crust and heated interior are composed of a variety of ele- 
mentary and compound substances. Elementary substances are 
those which have never been separated into components. Com- 
pound substances are those composed of two or more elementary 
substances combined under the influence of the chemical force. 



40 PHYSICAL GEOORAPEY. 

SECTION I. 
THE INSIDE OF THE EARTH. 

CHAPTER I. 

The Heated Interior. 

31. The Earth Originally a Fluid Mass.— There is but little 
doubt that our earth was originally intensely heated throughout its 
entire mass. Its present spheroidal shape, which is that of all the 
heavenly bodies, is what it would have assumed on account of its 
original molten condition. 

The original molten condition of the earth is in accordance with 
Laplace's nebular hypothesis ; for, as we have seen, if this hypoth- 
esis is correct, the temperature of the earth at the time of its separa- 
tion from the nebulous sun, must have been sufficiently high not 
only to melt, but even to volatilize all its materials. 

32. The Heated Interior of the Earth. — During the enormous 
time that has elapsed since its separation from the nebulous sun, the 
earth has been losing heat and cooling. But whether this cooling 
has continued sufficiently to permit the entire mass to become solid 
throughout, or whether it has been confined to a comparatively thin 
crust, is unknown. That the interior of our earth is still highly 
heated appears evident, however, from the following facts : 

(1) The deeper we penetrate the criist the higher the temperature 
becomes. The rate of increase of temperature varies in different 
localities, depending on how readily the different parts of the crust 
will permit heat from the interior to pass through it. On the aver- 
age, however, the heat increases about 1° F. for every 55 feet. This 
occurring in practically all parts of the earth, would seem to indi- 
cate that the entire inside of the earth is heated, and that the heat 
increases in intensity as we approach the centre. 



THE HEATED INTERIOR. 41 

(2) In all latitudes prodigious quantities of melted rock or lava 
escape from the interior either through fissures in the crust or through 
the craters of volcanoes. This lava comes from inside the earth, where 
the heat, consequently, must be sufficient to melt rock. 

(3) Careful geological observations prove that the earth's surface is 
never at rest. It is gradually rising in some places and sinking in 
others. Moreover, there is abundant evidence to show that such 
movements have continued throughout all geological time. These 
gradual changes of level are apparently due to the warping of the 
earth's crust consequent on the gradual loss of heat, and it would 
appear that they can be explained only by the theory of a heated 
globe gradually cooling. 

33. Condition of the Interior of the Earth. — We are ignorant 
of the present condition of the interior of the earth. Is it all highly 
heated ? Is the heat sufficiently great to melt all its ingredients, or 
is it in a molten condition only in part? 

If the rate of increase of temperature with descent below the sur- 
face continues uniform, and if substances below the earth's surface 
melt at the same temperature as they do at its surfac3, temperatures 
would be reached, at depths of from 30 to 50 miles, at which all 
known materials would be fused. But we know nothing about the 
rate of increase, except for very small depths, the greatest distance 
man has penetrated the crust of the earth — a few miles at the most 
— being insignificant as compared with the 4000 miles of the earth's 
radius. 

Nor is the fusing point of substances below the earth's surface 
the same as at its surface. The enormous pressure to which such 
substances are subjected necessitate a greater heat to fuse or melt 
them. And this increase may be so marked at profound depths 
that it may be necessary to assume a greater thickness for the 
earth's crust than has generally been imagined, or indeed, as is the 
opinion of many, there may be no liquid interior at all. 

In the opinion of able mathematicians and physicists, our earth 
acts, under the attraction of the sun and moon, not like a yielding 
liquid globe ; i. e., a fused globe covered by a thin, solid crust, but 



42 PHYSICAL GEOGRAPHY. 

rather as a globe that is rigid throughout. This has led them to 
reject the theory of a fused globe with a comparatively thin crust. 

These apparently hopelessly opposite conclusions of the astron- 
omer and geologist, concerning the condition of the earth's interior, 
may, nevertheless, says Russell, be harmonized. Perhaps the major- 
ity of leading geologists now believe that the earth is practicall) 
solid throughout. That its interior though solid, is nevertheless, 
potentially plastic; i. e., is sufficiently heated to become plastic and 
melt, provided the enormous pressure to which it is subjected is 
sufficiently decreased. Or, in other words, that the earth consists 
of a comparatively thin, rigid, cooled, and solid shell or crust, em- 
bracing a rigid, solid, but potentially plastic, heated interior. 

Some geologists have preferred to modify the above belief in the existence 
of a highly-heated and potentially plastic interior by assuming that the earth is 
solid throughout, with a liquid or pasty layer between the solid crust and the 
solid interior. It is difficult, however, to see how an originally molten globe 
could have cooled in this manner. 

34. Various Hypotheses of Condition of Interior. — Various 
hypotheses have been proposed to account for the heat of the inte- 
rior and the escape therefrom of melted rock or lava. Some of 
these are as follows : 

Chemical Hypothesis. — Davy and others regarded the heat as due to the 
action of water on unoxidized alkaline metallic substances, with which he 
assumed the earth's surface to be filled. This hypothesis is now discredited. 

Mechanical Hypothesis. — Mallet suggested a mechanical hypothesis in 
which the heat requisite for the melting of the rock is derived from the move- 
ments which occur when rocks are folded or faulted. That such friction might 
produce heat sufficient to melt rock would appear possible, but the hypothesis 
fails to explain, apart from a heated interior that is gradually cooling, the origin 
of the force which causes the folding or faulting. 

Aqueo-Igneous Hypothesis. — Shaler and others believe the accumulations 
of sediment, on sea-bottoms, would become highly heated by the heat from the 
interior by reason of the blanketing effect so exerted. While such an accumu- 
lation of heat might result in temperatures sufficiently high to account for erup- 
tions of hot mud, and for fusion of certain rocks in the presence of highly-heated 
steam, yet they would not be sufficiently high to account for true igneous 
fusion. 



THE HEATED INTERIOR. 43 

35* Thickness of the Crust. — It is evident that we cannot 
assign any definite limit to the thickness of the earth's crust, mean- 
ing by the word crust the outer portions of the earth that have 
become solidified by cooling, because these portions most probably 
pass insensibly into those that have become solid through loss of 
heat and increased pressure. It seems probable, however, that the 
part solidified by cooling is small, compared with the entire bulk of 
the earth; or, in other words, the potentially plastic or heated 
interior lies comparatively near the cooled crust. 

Effects of the Heated Interior. — In the remote geological past 
the cooling and consequent contraction of the molten earth produced 
a direct pressure on the interior. At the present time the cooled 
part of the earth or crust is a solid, rigid mass, not directly affected 
by the contraction of the heated mass within. When the heated 
interior cools it contracts and shrinks away from the solid crust, 
which adjusts itself to the new conditions by settling in the space 
left by the shrinking interior. This settling of the crust is accom- 
panied by flexures, bendings, and fractures, attended by changes of 
level of the earth's surface. Any. fracture extending through the 
crust to the potentially plastic interior acts as a relief of pressure, 
thus permitting a portion of the interior at that place to assume the 
molten condition, and, under the pressure to which the interior is 
subjected, either to fill the line of fracture, or even to pass through 
and escape at the surface. 

The molten matter may escape either in fissure or sheet eruptions, 
or in crater or volcanic eruptions. Moreover, both gradual and 
sudden changes of level may attend the cooling and shrinking of 
the interior. 

The gradual cooling of the heated, potentially plastic interior may, 
therefore, produce four different classes of effect : 

(1) Crater or Volcanic Eruptions; 

(2) Fissure or Sheet Eruptions; 

(3) Gradual Changes of Level ; 

(4) Earthquakes. 



44 



PHYSICAL GEOGRAPHY. 



CHAPTER II. 

Volcanoes. 
36. A Volcano is a mountain or other elevation, more or less 
conical near the top, provided with an opening or crater, through 

which, from time to 
time, vapors, ashes, 
and lava escape. 
The crater may be 
either on the top or 
on the sides of the 
mountain. 

37. Crater or 
Volcanic Erup- 
tions. — In crater or 
volcanic eruptions 
the lava flows 
through chimneys 
and builds up lava 
cones at the crater 
or point of escape. 
The conical shape is due to the ejected material accumulating around 
the mouth of the crater in more or less concentric layers. 

Crater, or volcanic eruptions, are distinguished from fissure or 
sheet eruptions by the fact that in crater eruptions the lava escapes 
in streams, while in fissure eruptions it escapes in sheets. 

38. Peculiarities of Craters. — The crater, as its name indicates, is cup- 
shaped. The rim is sometimes broken by the force of the eruption, as in Mount 
Vesuvius, where the eruption of 79 A. D. — the first on record — blew off the north- 
ern half of the crater. The material thus detached, together with the showers 
of ashes and streams of mud and lava, completely buried the cities of Hercula- 
neum and Pompeii, situated near its base. 

The crater is often of great size. Mauna Loa, on the island of Hawaii 
has two craters — one on the summit, and the other on the mountain-side, about 
4000 feet above the sea. The latter — Kilauea — is elliptical in shape, and about 
7i miles in circumference ; its area is nearly 4 square miles, and its depth, from 
600 to 1000 feet. 




Fig. 20. — The Cone of Mayon Volcano in the 
Philippines. 



VOLCANOES. 45 

39. Calderas or Crater Rings are deep, circular depressions 
formed on volcanic mountains either — 

(1) By the blowing away of a portion of the cone; or, 

(2) By the caving-in of the crater floor, owing to the absence of 
supporting lava beneath,. A caldera, now filled with water, is seen 
in Crater Lake, Oregon. 

40. The Ejected Materials are mainly as follows : 

(1) Melted Rock, or Lava. — Lava varies, not only with the 
nature of the materials from which it was formed, but also with the 
conditions under which it has cooled, and the quantity of air or 
vapor entangled in it. Though usually of a dark gray, it occurs in 
various colors. Its texture varies from hard, compact rock to 
porous, spongy material that will float on water. 

When first emitted from the crater, ordinary lava flows about as fast as molten 
iron would on the same slope. On steep mountains, near the crater, the lava, 
when very hot, may flow faster than a horse can gallop ; but it soon cools and 
becomes covered with a crust that greatly retards the rapidity of its flow, until 
its motion can be determined only by repeated observations. 

At Kilauea, jets of very liquid lava are sometimes thrown out, which, while 
falling back into the crater, are drawn out by the wind into fine threads, thus pro- 
ducing what the natives call Pele's hair, after their mythical goddess. 

The volume of the ejected lava is often very great. Volcanic islands are usually 
formed entirely by lava streams. Hawaii and Iceland were, probably, formed 
entirely of lava emitted from numerous volcanic cones. 

(2) Ashes or Cinders consist of minute fragments of lava that 
are ejected violently from the crater ; at night they appear as showers 
of brilliant sparks. When they fall directly back on the mountain, 
they aid in rearing the cone. The ashes, when exceedingly fine, 
form what is called volcanic dust, clouds of which give rise to the 
erroneous idea that smoke issues from the crater. 

At the beginning of an eruption large fragments of rock are some- 
times violently thrown out of the crater. 

Volcanic dust is often carried by the winds to considerable distances from the 
crater. In warm, moist climates the layers of volcanic dust that cover the 
ground, in volcanic districts, decompose and form an excellent natural fertil- 
izer. When mixed with lake sediment, as is the case in some of the north- 
western parts of the United States, it forms a wonderfully fertile soil. 



46 PHYSICAL GEOGRAPHY. 

(3) Vapors or Gases. — The vapor of water, the principal vapor, 
often escapes in great quantities from the crater, especially at the 
beginning of the eruption. On cooling, it condenses and forms 
clouds, from which torrents of rain fall. These clouds, lighted 
by the glowing fires beneath, appear to be actually burning, and 
thus give rise to the erroneous belief that a volcano is a burning 
mountain. To the condensation of this vapor is, probably, to be 
ascribed the lightning which often plays around the summit of the 
volcano during an eruption. Besides the vapor of water, various 
gases escape, of which sulphurous acid is the most common. On 
Mount Erebus, a volcano in the Antarctic, the vapor is condensed 
into snow, which reaches the ground before melting. 

Vent holes called fumaroles are formed in' the hardened crust over the recently 
ejected lava streams. Through them heated gas and vapors escape, from the 
glowing lava below, long after it has ceased to flow. Miniature craters are 
often formed around these openings. 

When rain mingles with the ashes, torrents of mud are formed, which move 
rapidly down the slopes of the mountain, occasioning considerable damage. The 
rock that is formed by the hardening of volcanic mud is called tufa. 

41. The inclination of the slopes of volcanic cones depends 
on the nature of the material of which they are formed. Where 

lava is the main ingredient, 
the cone is broad and fiat. 
The inclination of a lava 
cone ranges from S° to 10°, 
according to the liquidity of 
the lava. A very stiff lava will form a much steeper cone. 

Ashes and cinders form steeper cones, whose inclinations range 
from 30° to 45°. 

The lower slopes of the mountain are not so steep, and often 
extend for considerable distances. Etna, though only 10,834 feet 
high, has a base of nearly 40 miles in diameter. 

The sides of volcanic cones are often rent during the eruption^ 
and the fissures filled with lava, which hardens and forms rocky 
ribs called dikes, as in Fig. 23. Sometimes the central cone becomes 
choked, and secondary or parasitic cones are formed. 



Fig. 21.— Lava Cone. Inclination from 
3° to 10°. 



VOLCANOES. 



47 




Fig. 22. — Ash Cone. Inclination from 30° 
to 45°. 



42. The Cause of Volcanic Eruptions. — The settling of the 
solid crust, as it tends to fill the space left by the shrinking, heated 
interior, is attended by bend- 
ings, foldings, and fractures. 
Any of these fractures that 
extends to the potentially 
plastic interior acts as a 
relief of pressure at this 
point, and permits the inte- 
rior to become actually plas- 
tic, or even highly fluid. The pressure on this fluid rock may cause it 
to fill up the fissure, and even to escape therefrom through openings 
in the crust. These openings, when local, constitute the craters of 
volcanoes. 

Nearly all volcanic eruptions are attended by the escape of large quantities 
of steam. This fact has led some to regard the pressure of steam as the principal 
cause of the lava rising from the plastic interior. Were this true, the rocks form- 
ing dikes should be vesicular, or filled with small air spaces, instead of being, 
as they are, compact and dense. It would appear, 
however, that molten rocks rising from great 
depths, on coming in contact with water in the 
rocks nearer the surface, might become more 
fluid, and be aided by the steam pressure to 
reach the surface. 

In the opinion of some geologists, all volca- 
noes are situated in fissures that are filled, 
through fissure eruptions, with lava that has 
come up from great depths, and, that long after- 
ward, the surface water, percolating through masses of still liquid rock, pro- 
duce secondary eruptions through craters. It is for this reason that fissure 
eruptions are sometimes called primary eruptions, and volcanic eruptions, sec- 
ondary eruptions. 

The temperature required to melt dry rock is far greater than when water is 
present. It has been shown that, in the presence of highly heated water, rocks 
containing much silica will fuse at 800° F. The same rocks, if dry, might 
require 2500° F. It has, therefore, been asserted that in the presence of highly 
heated water, aided by the heat of the still glowing lava, the neighboring strata 
might be fused, and caused to escape from the surface as lava streams. 

Following the best authorities, however, we may regard the prime 




Fig. 23. — Volcanic Dikes and 
Parasitic Cones. 



48 PHYSICAL GEOGRAPHY. 

cause of volcanic eruptions as the shrinkage or contraction of the 
heated interior. 

Cordier has shown that a radial contraction of the earth of but a single milli- 
meter (0.03937 inch) would be ample to supply matter for five hundred of the 
greatest known volcanic eruptions. 

43. Volcanic Eruptions may be divided into two classes : explo- 
sive and non-explosive. 

(1) Explosive eruptions are attended by the formation of quan- 
tities of highly heated steam. They are usually preceded by earth- 
quake shocks ; then large quantities of ashes are thrown into the 
air, and this is followed by the escape of lava streams which flow 
down the mountain. 

On account of the great viscidity of some lavas, the evolved gases accumulate 
until considerable force is acquired. At Kilauea, liquid jets are thrown upward 
to the height of 40 feet. With very viscid lavas, like those of Vesuvius, bubbles 
of enormous size are suddenly formed, which burst with almost incredible force. 
Cases are on record in which it is estimated the ashes were projected 10,000 feet 
above the mouth of the crater. 

Volcanic Bombs. — Masses of plastic lava called volcanic bombs are sometimes 
thrown far upward in the air during the explosive eruptions of volcanoes. 
Acquiring a rotary motion, they assume a spherical form, and, hardening 
before they reach the ground, retain a spherical shape. Sometimes, striking 
the ground before they completely harden, they assume a flattened, oval shape. 
Spherical lava balls are also sometimes produced by a rolling motion in the 
advance portions of a lava stream. 

(2) Non-explosive eruptions occur where the lava is more 
fluid, and there is an absence of suddenly formed water vapor, 
or gas. When the crater is near the top of a very high mountain, 
the lava escapes quietly through a fissure, which opens in the moun- 
tain-side at some lower level, by reason of the pressure exerted by 
the column of liquid lava. 

Since a column of lava 500 feet high exerts a pressure of about 625 pounds to 
the square inch, when the mountain is high, the pressure against the sides of the 
crater may be sufiicient to rend the solid rock. 

The eruptions of Vesuvius furnish examples of explosive eruptions ; those of 
Kilauea and Etna, of non-explosive eruptions. 

44. Submarine Volcanoes. — Volcanoes are of common occur- 



VOLCANOES. 49 

rence at the bottom of the ocean. These are called submarine vol- 
canoes. L»uring eruptions their cones sometimes project auove the 
water ; but usually they soon disappear. 

45. Active and Extinct Volcanoes. — Volcanoes may be clas- 
sified as active and extinct. 

Active Volcanoes are those which emit vapor, ashes, or lava 
from the crater. 

The tubes or passage-ways, through which the lava flows from 
great depths to the surface, are usually left filled with lava when 
the volcanoes cease to be active. Slowly cooling and hardening, 
they form what are called volcanic necks. In the old age of vol- 




Fig. 24.— Volcanic Necks, New Mexico. 

canic mountains, when their outer layers have been gradually worn 
away or denuded, these volcanic necks or cones remain and form 
prominent features in the landscapes. Many such exist in New 
Mexico. 

The crater of an active volcano may at any time become permanently choked, 
and the volsano become extinct. Any volcano which has ceased to erupt during 
historical times is said to be extinct. It may, however, open at any time, after 
extended intervals of rest, when the volcano again becomes active. 
4 



50 PHYSICAL GEOGRAPHY. 

46. The number of volcanoes is not accurately known. The 
best authorities estimate it at about 672, of which 270 are active. 
Of the latter, 175 are on islands, and 95 are on the coasts of the 
continents. 

47. Reg-ions of Volcanoes. — The principal volcanic regions of 
the earth are — 

(1) Along the Shores of the Pacific Ocean, which is encircled, 
with but few breaks, by an immense chain of volcanoes. 

On the Eastern Borders of the Pacific, in the Andean range, are 
the volcanic series of Chili, Bolivia, and Ecuador ; those of Central 
America and Mexico ; in the United States are some recently extinct 
craters in the Sierra Nevada and Cascade ranges and in Alaska; 
and, finally, connecting the system with Asia, the volcanic group of 
the Aleutian Islands. 

According to Eussell, there are no recently active volcanoes from Central 
Mexico north to Southeastern Alaska, though there are many recently extinct 
craters, as well as hot springs and geysers. 

On the Western Borders volcanoes occur in the following districts : 
the Kamtchatkan Peninsula, Corea, with the submerged ranges of 
the Kurile Islands ; the Japan, the Loo Choo, and the Philippine 
Islands ; the Moluccas ; the Australasian Island Chain, terminating 
in New Zealand ; and, finally, nearly in a line with these, the vol- 
canoes of Erebus and Terror on the Antarctic continent. 

(2) In the Islands of the Pacific. — Volcanic activity is not 
wanting over the bed of the Pacific. The Sandwich Islands, the 
Society Group, the Marquesas, the Friendly Islands, the New Heb- 
rides, the Ladrones, and many others, are volcanic. 

(3) Scattered over the seas that divide the Northern and 
Southern Continents, or in their vicinity : 

In the Neighborhood of the Caribbean Sea. — This region includes 
the two groups of the Antilles in the Caribbean Sea, and the Galla- 
pagos Islands in the Pacific Ocean. 

Bi the Neighborhood of the Mediterranean and Red Seas. — This 
region includes the volcanoes of the Mediterranean and its borders, 



VOLCANOES. 



51 



those of Italy, Sicily, the Grecian Archipelago, and of Spain, together 
with those near the Caspian and Red Seas. 

Between Asia and Australia. — This region includes the Sunda 
Islands, Sumatra, Java, Sumbawa, Flores, and Timor. In this 
region there are numerous active craters. In Java there are nearly 
50 volcanoes, 28 of which are active, and there are nearly as many 
in Sumatra. There are 109 volcanoes in the small islands near 
Borneo. 

(4) In the Northern and Central Parts of the Atlantic 
Ocean. 

All the islands in the deep ocean, which do not form a part of the 
continent, are volcanic ; as the island of St. Helena, Ascension 
Island, the Cape Verdes, the Canaries, the Azores, and Iceland. 




Fig, 25.— Fuji Yama, a Comparatively Recent Volcano. 

The Cameroons Mountains, on the African coast near the Gulf of 
Guinea, together with some of the islands in the gulf, are volcanic 



52 PHYSICAL GEOGRAPHY. 

(5) In the "Western and Central Parts of the Indian 
Ocean. 

Volcanoes are found in Madagascar and in the adjacent islands. 
They also occur farther south, in the island of St. Paul and in Ker- 
guelen Land, and in Mount Kilimandjaro, near the eastern coast of 
Africa. 

48. Submarine Volcanoes.— From the difficulty in observing submarine 
volcanoes they are not so well known as the others. The following regions 
are well marked : 

In the Mediterranean Sea, near Sicily and Greece. 

In the Atlantic Ocean ; oflF the coast of Iceland ; near St. Michael, in the 
Azores ; and over the narrowest part of the ocean between Guinea and Brazil. 

In the Pacific Ocean ; near the Aleutian Islands, where two large moun- 
tain-masses have recently risen from the water ; and near the Japan Islands, 
where, about twenty-one centuries ago, according to native historians, Fuji Yama 
(Fig. 25), the highest mountain in Japan, rose from the sea in a single night. 

In the Indian Ocean, the island of St. Paul, in the deep ocean between 
Africa and Australia, exhibits signs of submarine activity. 

49. Peculiarities of Distribution. — Nearly all volcanoes are 
found near the shores of continents or on islands. 

It was formerly believed that this distribution showed the cause of eruptions 
to be the access of sea-water to the interior. The general belief now is that this 
distribution is due to the fact that the earth's volcanoes lie along lines of original 
fractures in the earth's crust, and that these lines are not necessarily dependent 
on the present distribution of the land and water areas. Moreover, there exist 
lines of fracture, with either recently active or still active volcanoes, at con- 
siderable distances from the coast, such as the Great Basin District in the United 
States ; in parts of Mexico and Central America ; and in Thibet. 

In most regions the volcanoes lie along lines more or less straight. 
Lines joining such a series may be considered as originally huge 
fissures in the crust, the volcanoes occurring in their weakest places. 

Where one system of fissures crosses another, as in the Antilles, and 
in the Sunda Islands, points that are almost antipodal to each other, 
the volcanic activity is unusually great. 

50. Life History of a Volcano (after Russell). — The birth of a volcanic 
mountain is usually preceded by severe earthquake shocks resulting in the forma- 
tion of a fissure and a forcing of the potentially plastic heated interior into the 
fissure. This may result either in a fissure eruption, or in a local or crater 

, eruption. The above phenomena attended the few volcanic mountains which 



VOLCANOES. 



53 



-lu fissure eruptions the lava 



ST^v^'Sff; 



have been born within historic times, such as Monte Nuovo, near Naples, in 1538, 
and JoruUo, in Mexico, in 1759. The accumulation of lava and ashes around 
the crater usually results in the formation of a conical mountain, though the 
shape will, of course, depend on the conditions and character of the material 
ejected. As the volcano grows in height its activity becomes more and more 
marked, and the eruptions increase in number and severity. Then follow long 
periods of rest, during which the volcano appears to have passed into hop less 
old age, when, suddenly, violent shocks again occur, and terrific explosions may 
blow oflf the top of the mountain, or rend vast fissures in its sides, and the vol- 
cano renews its youthful activity. These alternate periods of rest and activity 
may follow one another many times, but. the eruptions become less and less 
marked, the lava-flows are replaced by sulphurous vapors and steam, until 
finally, even marked heat ceases, and the volcanic mountain is no warmer 
than the surrounding country. 

Meanwhile erosion is taking place, and when the mountain ceases to be 
added to by fresh material from without, degradation and denudation occur. 
Deep gorges are cut in the mountain, and finally it is either entirely re- 
moved, or there remains only the hardened volcanic neck to mark the place of 
its birth. 

51. Fissure or Sheet Eruptions, 
escapes through fissures in 
sheets, and spreads out in wide 
floods. 

True fissure eruptions have 
occurred only in the geological 
past. The lava in fissure erup- 
tions was more liquid than that 
issuing from most volcanoes. 
Fissure eruptions occur in 
three different forms : 

(1) Extensive vertical sheef^^ 
filling great fissures in the rocks 
of nearly all geological forma- 
tions. On cooling, the mass 
forms what is called a dike. 
Dikes vary in Avidth from a 
few inches to several yards. They are usually much harder than 
the rock through which they were forced, and, being less subject 
to erosion, often project considerably above the general surface. 



Fig. 26. 



-Basaltic Columns, Giant's 
Causeway. 



54 



PHYSICAL GEOGRAPHY. 



From their mode of formation, dikes are usually without traces 
of stratification, but, by cooling, a series of fractures are sometimes 
produced, giving to the dike a columnar appearance, the dike then 
consisting of basaltic columns. Fingal's Cave in Scotland and the 
Giant's Causeway in Ireland are noted examples. 

The intense lieat of the fused rock causes the rocks forming the boundary 
walls of dikes to be markedly changed by the heat. Limestone is often con- 
verted into marble, bituminous coal into anthracite, and sometimes into coke. 

(2) Extensive horizontal sheets forced between parallel strata, 
or spread out over the bed of an ocean, or other body of water, or 
poured out on the surface of the land in great sheets. 

(3) Dome-shaped masses. Instead of escaping at the surface, the 
lava merely lifts the upper strata, and accumulates locally in dome- 
shaped masses called laccoliths or laccolites ; i. e., lake-like expansions 
of the lava stream. Suh-tuherant mountains are caused by the 
dome-shaped swellings produced in the overlying strata by the 
laccoliths. 

Some of the most important fissure eruptions are as follows : 
(1) The Columbian lava fields in the northwestern part of the United States. 
This region covers an area of about 250,000 square miles in Northern California, 

Washington, Idaho, and Oregon, as 



shown in Fig. 27. The deposits 
are from 3000 to 4000 feet thick. 

(2) The Deccan Trap, a region 
equal to about 200.000 square miles 
in area, in the western part of Hin- 
doostan. The deposits are from 200 
to 600 feet thick. 

(3) The dikes and sheets of igne- 
ous rocks extending in North 
America for 1000 miles along the 
Atlantic slope from Nova Scotia 
to South Carolina. The area cov- 
ered was, probably, nearly equal 
to that of the Columbian lava, or 
the Deccan Trap, but much of this, 

however, is either buried beneath sedimentary deposits, or has been removed by 
erosion. The Palisades of the Hudson form a part of this lava sheet. At Jersey 
City its thickness is from 300 to 400 feet. 

Other, extensive deposits occur in Abyssinia, Cornwalls, Wales, Scotland, and 




Fig. 27.— Columbian Lava Fields. 



EARTHQUAKES. 55 

Ireland, as may be seen from a study of the map of the geological formations 
of the earth. 

52. Gradual Elevations and Subsidences. — During the cool- 
ing of the heated interior, changes of level take place slowly, but 
continuously, by which large portions of the surface are raised or 
lowered from their former positions. The rate of these movements 
is so very slow — probably never exceeding a few feet in a century — 
that they become apparent only after long intervals of time. 

Subsidences. — The following parts of the earth appear to be 
now sinking or subsiding ; viz., the northern parts of ISTorway and 
Sweden, the southwestern coasts of Greenland, the ISTorth American 
coast from Labrador to New Jersey. The bed of the Pacific over 
an area of some 6000 miles in length. 

Elevations. — The following parts appear to be slowly rising; 
viz., nearly all the islands and lands bordering on the Arctic 
shores of North America, Europe and Asia, Labrador, Hudson 
Bay, Newfoundland, and the Andes of South America. 



CHAPTER III. 

Earthquakes. 

53. Earthquakes are shakings of the earth's crust, of degrees 
varying in intensity from scarcely perceptible tremors to violent 
agitations that overthrow buildings and open huge fissures in the 
ground. They may either accompany volcanic eruptions, or they 
may occur independently of such eruptions. 

An earthquake is sometimes called a seismic throb or shock. 

During severe earthquakes considerable areas are permanently raised or low- 
ered. During an earthquake in South America, in 1835, the entire coast-line of 
Chili and Patagonia was elevated from 2 to 10 feet above the ocean level. During 
an earthquake in 1819, near the mouth of the Indus, a tract some 2000 square 
miles in area sunk and was converted into a salt lagoon, while a much larger 
area was elevated some 10 feet. 

54. Facts Concerning- Earthquakes. — A careful study of earth- 
quakes appears to establish the following facts : 



56 PHYSICAL QEOORAPHY. 

(1) The place or origin of the shock is situated not far below 
the earth's surface, but is near the surface, probably, never deeper 
than thirty miles, and often much less. 

(2) The area of disturbance depends not only on the energy 
of the shock, but also on the depth of its origin below the surface : 
the deeper the origin, the greater the area of disturbance. 

(3) The shape of the origin is usually that of a line, often many 
miles in length. 

(4) The direction of the motion at the surface is nearly upward 
over the origin, and more inclined as the distance from the origin 
increases. 

(5) The shape of the area of disturbance depends on the nature 
of the materials through which the wave is moving. If these are 
of nearly uniform elasticity in all directions, the area is nearly cir- 
cular; if more elastic in some directions than in others, the area 
is irregular in shape. 

55. Varieties of Earthquake Motion. — There are three varie- 
ties of earthquake motiou : 

(1) Explosive. — These are attended by a violent motion directly 
upward. During such shocks the crust is broken, and bodies are 
thrown upward in the air. 

(2) Wave-like, or horizontally progressive, like waves in water. 
Here the area of disturbance is great. 

(3) Rotary, or those attended by a whirling motion of the crust. 

Humboldt mentions an earthquake that happened in Chili where the ground 
was so shifted that three great palm trees were twisted around one another like 
willow wands. 

There are two kinds of movement transmitted through the crust during earth- 
quakes : these are the earthquake motion proper, and the motion that produces the 
accompanying sounds. 

56. The Velocity of Earthquake Motion varies according to 
the intensity of the shock and the nature of the material through 
which it is transmitted. No average result, therefore, can be given. 
Various observers have estimated it at from 8 to 30 miles per 
minute. 

57. The Sounds Accompanying Earthquakes vary both in 



EARTHQUAKES. 57 

kind and intensity. Sometimes they resemble the hissing noises 
heard when red-hot coals are thrown into water; sometimes they 
are rumbling, but more frequently they are of greater intensity, 
and are then comparable to discharges of artillery or peals of 
thunder. 

The confused roaring and rattling are, probably, caused by the different rates 
of transmission of the sound through the air and rocks. 

58. Duration of the Shocks. — The earthquake shocks which 
cause the greatest damage are of but short duration, usually lasting 
but a few seconds or minutes. Though the violence of the shock 
is soon passed, disturbances may occur at intervals of days, weeks, 
or even years. 

During the earthquake in Calabria, in 1783, when nearly 100,000 persons per- 
ished, the destructive vibrations lasted scarcely two minutes, but the tremblings 
of the crust continued long afterward. During the earthquake at Lisbon, in 
1755, when about the same number perished, the shock which caused the great- 
est damage continued but five or six seconds, while a series of terrible move- 
ments followed one another at intervals during the space of five minutes. 

59. The Cause of Earthquakes. — As we have seen, the earth's 
surface is subject to many gradual changes of level, due to the cool- 
ing and contraction of the heated interior, and the consequent crush- 
ing, flexing, and fracture of the solid crust. If the yielding of the 
crust to the force causing these movements is constant, the motion 
will be gradual, and only perceived at the surface after long inter- 
vals of time. If, however, the crust resists the effort to move it, the 
force accumulates until, finally, the crust yields suddenly by fracture 
or crushing. This yielding is attended by a jar or concussion which 
shakes the earth. This concussion is propagated through the crust 
until it reaches the surface and moves outward from the point of 
exit. Earthquake shocks may also be produced by the slipping of 
fissui'ed rocks, as they subsequently settle. 

If the theory of gradually accumulated strain be true, as it prob- 
ably is, the earth's crust must occasionally be in such a strained 
condition, that the slightest increase of force from within, or of 
diminished resistance from without, would disturb the conditions 
of equilibrium, and thus result in an earthquake. 



58 PHYSICAL GEOGRAPHY. 

60. Accumulated Strain Caused by Contraction consequent on cooling 
is well exhibited in the so-called "Prince Rupert's Drops," which are made by 
allowing melted glass to fall in drops through cold water. The sudden cooling 
of the outside produces forces which tend to compress the drop ; but. since these 
forces balance one another, no movement occurs until, by breaking off the long 
end of the drop, one set of forces is removed, when the others, no longer neu- 
tralized, tear the drop into many pieces. 

61. Other Causes of Earthquakes. — Earthquakes may also be 
occasioned by — 

(1) The sudden formation and collapse of steam iu subterranean 
regions. 

This is probably the cause of many of the slight shocks that occur 
in the neighborhood of active volcanic regions. 

(2) Shocks caused by falling masses. 

Those who deny the existence of a pasty interior, endeavor to explain 
the production of earthquakes by the shock caused by the gradual settling 
of the upturned strata in mountainous districts. There can be no doubt that 
even moderately severe shocks are caused by falling masses ; but such a force 
is utterly inadequate to produce severe earthquake shocks like that, for exam- 
ple, which destroyed Lisbon, when an area of nearly 7,500,000 square miles was 
shaken. 

62. Periodicity of Earthquakes. — Although earthquakes may 
occur at any time, yet by a comparison of the times of occurrence 
of a great number it appears that they occur more frequently — 

(1) In winter than in summer; 

(2) At night than during the day ; 

(3) During the new and full moon, when the attractive force 
of the sun and moon acts simultaneously on the same parts of the 
earth. 

Earthquake shocks are more frequent in winter and during the night, because 
the cooling, and consequent contraction, occur more rapidly at these times, and, 
therefore, the gradually accumulating force is more apt to acquire sufficient 
intensity to rend the solid crust. 

Earthquakes are more frequent during new and full moon, because the 
increased force on the earth's crust, caused by the position of the sun and moon 
at these times, is then added to the accumulated force produced by cooling. 

63"64. Distribution of Earthquakes.— Earthquakes may occur 
in any part of the icorld, but are most frequent in volcanic districts. 




K j;!^" S,Ly-\\. "i^SANTA CRUZ I 







V 

^'J-Vtahit' 



TROPIC 





l-'s, 



CAPRICORN 

C E 



GALLAPACOS IS. 



Arequipa 



_UuJ[aya 



A ]Sf 



I: t 



MAP OF THE WORLD 

SHOWING THE DISTRIBUTION OF 

VOLCANOES 

AND REGION OF 

EARTHQUAKES. 



Osorno). 



Sarmiento^ 



A 



R 




REFERENCES 

I I VOLCANIC REGIONS. 



3 EARTHQUAKE REGIONS. 



Frequency of shocks indicated by depth of shading 
ACTIVE VOLCANOES :: EXTINCT VOLCANOtS+V 



E 



• K [RGUELEN LAND 



.'^ 



N 



lOngitude 40 West from 20 Greenwich Longitude 20 East from 40 Greenwich GO 



EARTHQUAKES. 



59 



They are more frequent in mountainous than in flat countries. 
They are especially frequent in high mountains, while yet in the 
process of gradual elevation. According to Huxley, fairly pro- 
nounced earthquake shocks occur in some part of the earth at least 
three times a week. 

There is, in many instances, an undoubted connection between volcanic erup- 
tions and earthquakes. Humboldt relates that during the earthquake at Eio- 
bamba, when some 40,000 persons perished, the volcano of Pasto ceased to emit 
its vapor at the exact time the earthquake began. The same is related of Vesu- 
vius at the time of the earthquake at Lisbon. 







•^'^ f-'' <&«»> 



Fig. 27a. — The Effect of an Earthquake Shock on a Church in Costa Rica. 

<K>>J400 



SYLLABUS. 

The earth's original fluidity is probable because — 

(1) The deeper we penetrate the crust, the higher the temperature becomes. 

(2) In all latitudes prodigious quantities of melted rock or lava escape from 
the interior of the earth either through fissures or through craters. 

(3) Careful observations prove that the earth's surface is never at rest. 

The interior is still in a highly heated condition. This is proved — (1) By the 



60 PHYSICAL OEOGRAPHY. 

increased heat of the crust as we go below the surface ; (2) By the escape of lava 
in all latitudes. 

It is generally believed that the earth is practically solid throughout ; that 
its interior, though solid, is potentially plastic ; i. e., sufficiently heated to become 
plastic, or even to melt, when the great pressure to which it is subjected is suf- 
ficiently decreased. 

The gradual cooling of the potentially plastic interior may produce: (1) Crater 
or volcanic eruptions ; (2) Fissure or sheet eruptions ; (3) Gradual changes of 
level ; (4) Earthquakes. 

The ejected materials of volcanoes are — (1) Melted rock or lava; (2) Ashes or 
cinders ; (3) Vapors or gases. The inclination of the slopes of a volcanic cone 
depends on the material of which it is composed. Ash-cones are steeper than 
those of lava. 

Eruptions are of two kinds, explosive and non-explosive. 

Volcanoes occur both on the surface of the land and on the bed of the ocean. 

The principal volcanic districts of the world are — (1) Along the shores of the 
Pacific; (2) On the islands which are scattered over the Pacific; (3) Scattered 
over the seas which divide the northern and southern continents; (4) In the 
northern and central parts of the Atlantic Ocean ; (5) In the western and cen- 
tral parts of the Indian Oceau. 

The centres of volcanic activity are found in the Antilles and in the Sunda 
Islands, where several lines of fracture cross each other. 

Fissure or sheet eruptions occurred only in the geological past, as (1) Exten- 
sive vertical sheets in great fissures in the rocks of nearly all geological forma- 
tions ; (2) Extensive horizontal sheets between parallel strata or spread out over 
extended areas ; (3) In dome-shaped masses or lake-like expansions called lacco- 
liths or laccolites. 

Dikes are masses of rock formed by the gradual cooling of melted matter 
which has been forced up through fissures from the interior. Basaltic columns 
are formed by dikes. Basaltic columns owe their columnar structure to fractures 
produced on cooling. 

The following parts of the earth are slowly sinking ; viz., the northern parts 
of Norway and Sweden ; the southwestern coasts of Greenland, the North Amer- 
ican coast from Labrador to New Jersey ; the bed of the Pacific. 

The following parts are slowly rising ; viz., nearly all the islands and lands 
on the Arctic shore of North America, Europe, and Asia ; Labrador, Hudson 
Bay, Newfoundland, and the Andes in South America. 

Earthquakes are shakings of the earth's crust; they may occur with or with- 
out a permanent displacement. 

The following facts have been discovered as to earthquakes : 

(1) Their place of origin is not deep-seated. 

(^) The area of disturbance increases with the energy of the shock and the 
depth of the origin. 



SYLLABUS. 61 

(3) The shape of the origin is that of a line, not of a point. 

(4) The direction of the motion is nearly upward. 

(5) The shape of the area of disturbance depends on the elasticity of the 
materials through which the shock moves. 

There are three varieties of earthquake motion ; (1) Explosive ; (2j Wave-like ; 
(3) Eotary. 

There are two distinct kinds of motion accompanying earthquake waves: 
the earthquake motion proper, and the motion producing the accompanying 
sounds. 

The velocity with which the earthquake motion is transmitted varies with 
the intensity of the shock and the nature of the materials traversed. 

As a rule, the earthquake shocks which produce the greatest damage are of 
but short duration, generally but a few seconds or minutes. Slighter disturb- 
ances may follow the main shock at intervals of days, weeks, or even years. 

Earthquakes are mainly caused by the gradually increasing force produced 
by the contraction of the crust. They are also caused by the slipping of fis- 
sured rocks, as they subsequently settle ; by the sudden formation and col- 
lapse of steam in subterranean regions; and by the shock caused by falling 
masses. 

Earthquake shocks are more frequent — (1) In winter than in summer; (2) At 
night than during the day ; (3) During the time of new and full moon than at 
any other phase. 

Earthquakes may occur in any part of the world, but are most frequent in 
volcanic and in mountainous regions. 

REVIEW QUESTIONS. 

The Heated Interior. 

Why is it probable that the earth was originally molten throughout? 
Enumerate the proofs that the interior of the earth is still in a highly heated 
condition. 

What is meant by a potentially plastic interior? 

What four classes of efiects are produced in the crust by the heated interior? 

Volcanoes. 

What are volcanoes ? In what respect do active volcanoes differ from those 
which are extinct? 

Explain in full the manner in which the shrinkage or contraction of the 
earth on cooling produces volcanic eruptions. 



62 PHYSICAL GEOGRAPHY. 

Into what two classes may all volcanic eruptions be divided ? How are those 
of each class caused ? Give an example of each class. 

Under what five regions may all the volcanoes in the world be arranged ? 

Name some of the regions of submarine volcanoes. 

Give a brief statement of the life history of a volcano. 

What are dikes? How were they formed ? 

Distinguish between crater or volcanic eruptions and fissure or sheet erup- 
tions. In what three different forms do fissure or sheet eruptions occur ? 

Describe the Columbian lava-fields. The Deccan Trap region. 

Enumerate some of the gradual changes of level which are now occurring in 
the crust of the earth. By what are these changes caused ? 

Earthquakes. 

What are earthquakes ? 

Name some facts that have been discovered about earthquakes. 

Name three kinds of earthquake motion. Which is the most dangerous? 

What is the main cause of earthquakes ? To what other causes may they be 
attributed? What facts have been discovered respecting their periodicity? 

Give a short description of the earthquake which destroyed the city of 
Lisbon. In what parts of the earth are earthquake shocks most frequent? 

<«)J»^00 



MAP QUESTIONS, 



Trace on the map the five principal volcanic districts of the earth. 

Does the eastern or the western border of the Indian Ocean contain the greater 
number of volcanoes ? 

Name the principal volcanic islands of the Atlantic Ocean. Of the Indian. 
Of the Pacific. In what part of the Atlantic Ocean are submarine eruptions 
especially frequent? 

Locate the following volcanoes : Hecla, Pico, Kilauea, Sarmiento, Llullayacu, 
Egmont, Cosiguina, Tenerifle, Antisana, Kilimandjaro, Demavend, Peshan, 
Osorno, Erebus, and Terror. 

Name the portions of the earth shaken by the earthquake of Lisbon. What 
noted volcanoes are found in the region of the earthquake of Lisbon ? 



SECTION II. 
THE OUTSIDE OF THE EARTH, 

CHAPTER I. 

The Crust of the Earth. 

65. Composition of the Crust. — The elementary substances- 
are not equally distributed throughout the earth's crust. Many 
occur only in extremely small quantities, while others are found 
nearly everywhere. 

Although the deepest cutting through the earth's crust does not extend ver- 
tically more than about two miles below the level of the sea, yet the outcropping 
of the different formations enables us to study a depth of about sixteen miles 
of the earth's crust. 

Oxygen constitutes nearly one-half by weight of the known part of the crust. 
Silicon, which when combined with oxygen, forms silica or quartz, constitutes, 
either as sand, or combined with various bases as silicates, one-fourth ; so that 
these two elements form at least three-fourths, by i>:Aght, of the entire crust. 
The following are also prominent ingredients : aluminium, which when combined 
with oxygen, forms alumina, the basis of clay, and magnesium, calcium, potassium, 
sodium, iron, and carbon. The above enumerated nine elements, according to 
Dana, form ^^'^''^ths, by weight, of the entire crust. 

Sulphur, hydrogen, chlorine, and nitrogen also occur frequently. The remaining 
elements are of comparatively rare occurrence. 

66. Rocks. — In its geological sense, the word rock embraces 
various mixtures of substances called minerals, that occur naturally 
in sufficient masses to be properly considered as an essential part 
of the crust. This includes not only the hard strata, but also the 
softer beds of sand and clay. 

Minerals consist of fairly definite chemical compounds. Though 

63 



64 PHYSICAL OEOQRAPHY. 

rocks sometimes consist of a single mineral, they are usually formed 
by mechanical mixtures ©f two or more minerals. 

Some of the more important mineral constituents of the crust are 
felspar, quartz, mica, soapstone, limestone, and clay. 

Clays containing an excess of finely divided silica are called 
fuller's earth; when mixed with a certain proportion of fine sand, 
they form what is called foam, and when containing a certain pro- 
portion of calcium, are called marl. 

Kocks may be divided into different classes : (1) According to 
their origin or the manner in which they were formed ; (2) Accord- 
ing to their condition or the way in which their mineral ingredients 
are arranged ; and (3) According to the presence or absence of 
organic remains. 

67. According to their Origin, rocks may be divided into three 
distinct classes : igneous, aqueous, and metamorphic. 

(1) Igneous Rocks are those which have been in a molten state, 
and have solidified on cooling. They include two classes : 

(a) Plutonic rocks, or those which have slowly cooled helow the surface under 
great pressure, and have solidified as crystalline rocks ; true granite is an 
example. 

(6) Volcanic rocks, or those which have erupted at the surface, and, having 
cooled rapidly and without pressure are, as a rule, devoid of crystalline form. 
Lava and basalt are examples. 

(2) Aqueous Rocks, or those deposited as sediment by water. 
When mineral matter settles in water, the coarser, heavier particles 
reach the bottom first, so that a sorting action occurs, which makes 
the different layers or strata vary in the size and density of their 
particles, and, to a great extent, in their composition. 

Aqueous rocks are sometimes called sedimentary rocks. 

(3) Metamorphic Rocks are those in which have occurred sucb 
marked chemical and mineral changes, produced by heat in the 
presence of moisture, together with pressure, that their original 
constitution has been more or less altered and their character 
disguised. Both sedimentary and igneous rocks are subject to 
these changes. 



THE CRUST OF THE EARTH. 



64a 




Fig. 27b.— Stratified Eock and Gravel, Arizona. 







Fig. 27c.— TJnstratified Igneous Rock, Nova Scotia. 



64b 



PHYSICAL GEOGRAPHY. 




Fig. 27d.— The Pillars of Hercules, Erosion Columns, Partly the Product of 
Wind Erosion. 



THE CRUST OF THE EARTH. 65 

The changes are in some cases so marked that it is difficult to distinguish 
between rocks of metamorphic and igneous origin. Many rocks which were for- 
merly believed to be of igneous origin, are now generally regarded as highly 
altered sedimentary strata. Even some granites are thought to be of meta- 
morphic origin. 

These changes, which are called metamorphisms, are caused by heat acting under 
pressure in the presence of moisture. Under these conditions a far less intense 
heat is required to remove all traces of stratification. Metamorphism appears to 
consist mainly in a rearrangement of the chemical constituents of the rocks. 

To the above are sometimes added an additional class ; viz., 
jEolian rocks, or those formed from wind drifted materials. They 
are irregularly bedded. 

68. According to their Condition, rocks may be divided into 
two classes : 

(1) Stratified Rocks, or those arranged in regular layers. 
Aqueous rocks are always stratified, and sometimes, though rarely, 
metamorphic rocks exhibit traces of stratification. 

(2) Unstratified Rocks, or those destitute of any arrangement 
in layers. They are of two kinds : 

(a) Igneous, or those which were never stratified. 

(b) Metamorphic, or those which were once stratified, but have 
lost their stratification by the action of heat. 

Unstratified rocks are sometimes called crystalline rocks, because 
they consist of crystalline particles. 

69. Primitive Rocks.— The earth's earliest or primitive rocks 
were either those formed by the first cooling and hardening of the 
outside of the melted earth, or those thrown down as sediment in 
the primitive ocean. The crust, however, has been so repeatedly 
fractured and broken up and thrown down as sediment, that it is 
practically certain that all traces of the original crust have long ago 
disappeared. The lowest rocks we have yet reached were originally 
deposited as sediment in water, and have been so modified by in- 
tense heat that they present nearly all the appearances of rocks 
formed by the cooling of melted matter. In other words, almost all 
rocks are fragmental; i. e., have been made out of the broken or 
worn fragments of older rocks. All beds of sand, gravel, stones. 



66 



PHYSICAL GEOGRAPHY. 




Fig. 28. 



mud, clay, and earth are merely worn, pulverized, or weathered 
rock, 

70. Fossils are the remains of plants or animals which have 
been buried in the earth by natural causes. Generally, the soft 

parts of the organism have 
disappeared, leaving only the 
harder parts. Sometimes the 
soft parts have been grad- 
ually removed, and replaced 
by mineral matter, such as 
lime or silica, thus produc- 
ing what are called petrifaC' 
tions. At times the mere 
impression of the animal or 
plant is all that remains to 
tell of its former existence. 

When the remains of an animal 
or plant are exposed to the air, or 
buried in dry earth, they usually 
decompose and pass off almost en- 
tirely as gases ; but when buried under water, or in damp earth, their preserva- 
tion is more probable. Therefore, the species most likely to become fossilized 
are those living in, or near, water or marshes. 

71. According- to the Presence or Absence of Fossil 
Remains, rocks may be divided into two classes : 

(1) Fossiliferous Rocks, or those which contain fossils. They 
are stratified, and are of aqueous origin. Metamorphic rocks, in 
rare instances, are found to contain fragments of fossils. 

(2) Non-fossiliferous Rocks, or those destitute of fossils. They 
include all igneous rocks and most of those that are metamorphic. 

72. Paleontology is the science which treats of the plants and animals 
whose remains are now found only as fossils. Paleontology enables us to ascer- 
tain the earth's condition in pre-historic times, since by a careful examination 
of the fossils found in any rocks we discover what animals and plants lived on 
the earth while such rocks were being deposited. The earth's strata thus become 
the pages of a huge book ; and the fossils found in them, the writings concerning 
the old life of the world. By their careful study geologists have been enabled to 
find out much of the earth's past history. 



-Plesiosaurus Macroceplialus 
(Buckland). 




120 Longitude 140 East from IGO Greenwich 180 



40 20 




1 ARCHAEIC AND GRANITES 
I PALAEOZOIC. 
I MESOZOIC. 



REFERENCES 

I 1 TERTIARY AND DESERT 

I I SAND STONES. 

^^Bl QUATERNARY. 

ilSl SANDY AND DESERT WASTES. 



FORMATIONS. 



ngitude 40 West from 20 Greenwich Longitude 20 East from 40 Greenwich 



THE CRUST OF THE EARTH. 67 

73. Division of Geological Time. — A comparison of the various 

species of fossils found in the earth's crust discloses the following 
facts : 

(1) The fossils found in the lowest rocks bear but a slight resem- 
blance to the animals and plants now living on the earth. 

(2) The fossils found in the intermediate strata bear a resem- 
blance to existing species, though this resemblance is not so strongly 
marked as in the upper strata. 

(3) The fossils found in the upper strata bear a decided resem- 
blance to existing species. 

It is on such a basis that the immense extent of geological time 
is divided into eras, the eras are subdivided into periods, the periods 
into epochs, and the epochs into ages. 

There are six geological eras : the Azoic, the Eozoic, the Palse- 
ozoic, the Mesozoic, the Cenozoic, and the Era of Man. 

As regards the enormous extent of geological time, Dana, reviewing the 
various estimates as to its duration, based on different physical phenomena, 
says: "The safe conclusion from all the geological and physical facts is that 
time is long, very long ; long enough for the development of all the earth's 
rocks, mountains, continents, and life. Geologists have no reason to feel ham- 
pered in their speculations, vphile the extreme results of calculation are 10,000,000 
and 6,000,000,000 years." 

74. The Azoic Bra. — The word azoic means no life. The name 
was applied to that extremely extended time that existed from the 
formation of the earth until the first appearance of life. It included 
the time when the temperature was so high as to have rendered the 
existence of life impossible. In certain formations, however, which 
were originally included in the Azoic Era, markings have been found 
that, in the opinion of some geologists, were due to the existence of a 
simple form of life ; therefore, toward the close of what has been 
included in the Azoic Era, life may have appeared. 

The Azoic Era included a long period during which our earth 
was a glowing star ; this period is, therefore, called the Astral Period, 
and a later period of the Azoic Era, whose boundaries have not yet 
been satisfactorily fixed, is called the Archaean Period. 

The Arehcean Period was intended to include the most ancient 



68 PHYSICAL GEOGRAPHY. 

rocks, the basement or fundamental rocks; i. e., igneous rocks that 
resulted from the cooling of the molten earth. The lowest known 
rocks of this period are fragmental, having been apparently formed 
from sedimentary deposition of the original archsean rocks. They 
are highly metamorphosed. 

In North America the lowest of the Archsean rocks include the 
Laurentian, so called from their occurrence in extensive deposits in 
the neighborhood of the St. Lawrence River. 

75. The Eozoic Era. — The word eozoie means the dawn of life. 
The name was applied to the time when life was first created. As 
already stated, this may have occurred toward the close of the 
Azoic Era. 

The Eozoic Era includes a period called by the United States 
Geological Survey the Algonkian Period. It comprises an extended 
series of sedimentary and metamorphosed rocks between the Archsean 
and the oldest of the Palaeozoic formations. They are represented 
in North America by the Huronian, so named from their occurrence 
in the neighborhood of Lake Huron. 

Most of the sedimentary rocks of the Eozoic Era are very highly metamor- 
phosed, so that remains of plants and animals are nearly obliterated. The 
occurrence in the rocks of graphite, a form of carbon, is regarded as strong evi- 
dence of plants, if not of animals. Algse or sea-weeds, among marine plants, and 
some of the lowest forms of the protozoa were, perhaps, abundant. 

76. The Palaeozoic Era. — The word palaeozoic means ancient life. 
The Palaeozoic Era embraces the time of ancient life, during which 

the plants and animals bore comparatively little resemblance to 
those now living. The deposits of Palaeozoic Time are sometimes 
called the primary. The duration of the Palaeozoic Era was, prob- 
ably, equal to that of both the Mesozoic and Cenozoic Eras. 
Palaeozoic Time includes the following periods : 

(1) The Silurian Period, or the Period of Invertebrates ; 

(2) The Devonian Period, or the Period of Fishes; 

(3) The Carboniferous Period, or the Period of Coal Plants. 

77. The Silurian, or the Period of Invertebrates, is sometimes 
called the Period of Mollusks. Among plants, algce, or sea-weeds, 



i 



THE CRUST OF THE EARTH. 



69 



are found ; among animals, protozoa, radiates, articulates, and mol- 
lusks, but no vertebrates. Hence the name, Period of Invertebrates. 
Mollusks were especially numerous. Vertebrates in the form of 
fishes appeared toward the close of this period. 

78. The Devonian, or the Period of Pishes. — During this 
period all the sub-kingdoms of animals are found. The vertebrates, 
however, represented by fishes, were the dominant type of life, and 
from this fact the name has been given to the period. Land-plants 
are also found. Immense beds of limestone and red sandstone 
were deposited. 

The name Devonian is derived from the district of Devonshire, England, 
where the rocks abound. 

79. The Carboniferous, or the Period of Coal-Plants. — Dur- 
ing this period the continents consisted mainly of fiat, marshy areas, 
covered with luxur- 
iant vegetation, sub- 
ject, at long inter- 
vals, to extensive 
inundations. The de- 
c a y i n g vegetation, 
decomposing under 
water, retained most 
of its solid constit- 
uent, carbon, and 
formed beds of coal. 
All the sub-kingdoms 
of animals were rep- 
resented, and reptiles 
also existed. The 
comparatively few 
land-plants of the preceding period now increased and formed a 
dense vegetation. 

Formation of Coal.— Every 100 parts of dry vegetable matter contains 
about 49 parts of carbon, 6 of hydrogen, and 45 of oxygen. Carbon is a solid ; 
hydrogen and oxygen are gases. It is from the carbon that coal is mainly 




Fig. 29.- 



-Carboniferous Landscape, 
ration. ) 



(A resto- 



70 



PHYSICAL GEOGRAPHY. 



formed. When the decomposition of the vegetable matter takes place in air, the 
carbon passes olf with the hydrogen and oxj^gen as various gaseous compounds ; 
but, when covered by water, most of the carbon is retained, together with part 
of the oxygen and hydrogen. Every year our forests drop immense quantities 
of leaves, but no coai results, the deposit of one year being almost entirely 
removed before that of the nest occurs. 

It has been computed that it would require a depth of eight feet of compact 
vegetable matter to form one foot of bituminous coal, and twelve feet of vege- 
table matter to form one foot of anthracite coal. Anthracite coal differs from 
bituminous mainly in the greater metamorphism to which it has been subjected J 
it contains a greater proportion of carbon and less hydrogen and oxygen. The 
latter part of the Carboniferous Period is now called the Permian. 

80. The Mesozoic Era, the middle era of geological time, whea 
the plants and animals began more closely to resemble those now 
living, includes the Triassic, the Jurassic, and the Cretaceous 

Periods. The deposits 
of the Mesozoic Era are 
sometimes called the Sec- 
ondary. The Mesozoic 
is sometimes called the 
Era of Reptiles. The 
era is characterized 
mainly by the prepon- 
derance of reptiles, many 
of which were very large, 
as, for example, the ple- 
siosaurus, an animal with 
a long, snake-like neck 
and a huge body, or the 
ichthyosaurus, with a 
head like a crocodile an i 
short neck and large body. Both of these animals were furnished 
with fin-like paddles, and lived in the water. Huge pterodactyls, 
or bat-like saurians, flew in the air or paddled in the water. Mam- 
mals and birds also occur. 

81. The Cenozoic Era, the era of geological time immediately 
preceding the present era, included the time during which animals 




Fig. 30. — Mastodon Giganteus. An Animal of 
the Mammalian Age. 



THE CRUST OF THE EARTH. 



71 



and plants bore decided resemblance to those now living. The 
Cenozoic Era includes the Eocene, the Oligocene, the Miocene, and 
the Pliocene Epochs. It is sometimes called the Era of Mammals, 
because mammals, or animals that suckle their young, occurred in 
great numbers, and* being the highest type of life, gave the name 
to the age. The animals and plants of the Mammalian Era closely 
resembled existing species, though most of them were much larger; 
as, for example, the dinotherium, a huge animal, with a trunk like 
an elephant, but with downward-turned tusks ; the palceotherium, 
and many others. 

82. The Era of Man, or the Quaternary, witnessed the intro- 
duction of the present animals and plants and the creation of man. 
It includes the Pleistocene Epoch, which in its turn embraces the 
pre-glacial, the glacial, and the post-glacial series. 

Table of Geological Divisions. 



Formations. 


Eras. 


Periods or Epochs. 


Quaternary 


Man. 


Pleistocene Epoch. 


r 
1 

Tertiary \ 

1 
1 

I 


r 

1 

Cenozoic. \ 
1 
I 


Pliocene Epoch. 
Miocene " 
Oligocene " 
Eocene " 


r 

Secondary . . . . j 

1 
I 


Mesozoic. 


Cretaceous Period. 
Triassic " 
Jurassic " 


r 

Primary \ 

I 


Palseozoic. 

Eozoic. 
Azoic. 


Permian Period. 
Carboniferous " 
Devonian " 
Silurian 

Algonkian " 
Archaean " 
Astral " 



83. Order of Earth's Strata. — Where no disturbing causes 
existed, and the land remained under the seas, the rocks deposited 



72 PHYSICAL GEOGRAPHY. 

during the preceding eras were thrown down in regular strata, one 
over the other. The Azoic were the lowest ; above them were the 
Eozoic, then the Palseozoic, the Mesozoic, the Cenozoic, and, finally, 
those of the present time. Frequently, however, dislocations of the 
strata have disturbed the regular order of arrangement. Some idea 
of this arrangement wilt be obtained from the table of geological 
divisions given on the preceding page. 

84. Agencies Now Producing Changes in the Earth's 
Crust. — It is evident that geological time was characterized by 
extensive changes, both in the kitid and luxuriance of life, and in 
the nature of its distribution. 

Changes are still occurring in the earth's crust, the agencies pro- 
ducing them differing in no respect, except in some instances in the 
intensity of their action, from those which were active in geological 
time. Many of these changes are so slow in their action that they 
require the great lapse of geological time to become apparent. 
Some, however, are sufiiciently marked to have been readily 
observed within historical time. 

The most important agencies that are now in operation are as 
follows; viz., the Heated Interior, Erosion or Denudation, includ- 
ing Weathering, Corrasion, and Transportation, Wind Corrasion 
and Transportation, Avalanches and Land-slides, Ocean Waves, 
and Man. 

85. The Heated Interior of the earth, which, while gradually 
cooling, is still producing earthquakes and volcanoes, and is still 
gradually raising some portions of the earth's surface and lowering 
others. 

86. The Erosion, Denudation, or gradual wearing away of the 
land uplifted above the sea-level. This action has taken place 
throughout the vast extent of geological time. By it, high moun- 
tains and portions of the continental masses, have been slowly carried 
piecemeal into the ocean. Erosion or denudation is still taking 
place at every exposed surface. Erosion is due to the action of 
three agencies ; viz.. Weathering, Corrasion, and Transportation. 

87. Weathering is the mechanical or chemical disintegration 



THE CBUST OF THE EARTH. 73 

of rocks by a series of complex processes. Whenever a rock sur- 
face is exposed to the action of the weather ; i. e., to the action of 
heat, moisture, air, and the alternate freezing of water and melting 
of ice, its surface either gradually cracks, splits, or is broken up into 
small fragments, or rusts, or is corroded and eaten away. When 
these fragments remain in place they protect, to a great extent, the 
rock surfaces below them from further action, but in nearly all cases 
they are carried away or transported either by gravity, by the wind, 
or by running water, thus permitting the weathering action to con- 
tinue indefinitely. 

Some of the more important agencies that cause weathering are : 

(1) Heat and Cold. — The alternate expansion and contraction 
of the rocks attending variations in temperature, under the varying 
action of the sun's heat, tend to break them up. In general, these 
diurnal changes in temperature do not extend much further than 
a few feet below the surface, and the annual changes not further 
than about 50 or 60 feet. 

The effect of heat is most marked in tropical climates, both by drying up 
large tracts of land, thus rendering them deserts, and, by depriving them of 
their protective covering of plants, promoting and aiding chemical and mechan- 
ical action. 

The effect of cold is most marked in arctic regions, vrhere the shrinkage 
suffices to break up the rocks, and this independently of the presence of moist- 
ure. This effect was especially observed by Kane in the wasting of the cliffs 
in North Greenland. 

(2) Alternate Freezing and Thawing. — In climates characterized 
by alternate freezing and thawing, water, soaking into porous rocks, 
or collecting in the crevices of impervious rocks, is a powerful 
agency in rending the rocks, since the water in freezing expands 
with a force sufficiently great to break the rocks into fragments. 
This cause is not so prominent in extremely high latitudes as it is 
in the less frigid regions. 

(3) Rusting, Corrosion, and Solution. — Either the air alone, or 
the air and its accompanying moisture, enter into chemical combi- 
nation with some of the substances in the rocks, thus gradually cor- 
roding or changing them into substances that are more readily 



74 



PHYSICAL GEOGRAPHY. 



carried away or dissolved by the percolating waters. The rain 
water which enters the ground is nearly pure water, and its solvent 
power for most mineral matters is very much less than when it con- 
tains certain foreign substances, such as carbonic acid or certain 
acids, derived from the soil through which it passes. Moreover, 
when heated, either by neighboring beds of recently ejected lava, 

or by reason of its sink- 
ing to great depths, its 
solvent, and, conse- 
quently, its corroding 
power, are very greatly 
increased. 

Water containing 
carbonic acid possesseo 
marked powers of dis- 
solving limestone rocks. 
The surface drainage is 
apt to be exceedingly 
limited in limestone 
districts, the streams 
being either scanty or 
entirely absent. The 
surface water entering 
the ground, dissolves 
out the limestone and 
forms what are called 
sink-holes. The under- 
ground water, following 
the lines of easiest pas- 
sage, dissolves out the 
Fig. 3l.-Natural Bridge, Virginia. limestone, thus forming 

true underground 
streams, and, by eating out the rock, forms immense caverns. 




Such caverns are found in tlie Mammoth Cave in Kentucky, and in the Luray 
Cave in Virginia. The water dripping from the roofs of the caves falls on the 



THE CRUST OF THE EARTH. 75 

floor beiow, and, on the partial evaporation of the water and the loss of carbonic 
acid gas, deposits the lime as icicle-like pendants from the roof, called stalactites, 
and sharp hillocks or mounds, immediately beneath, called stalagmites. The 
meeting of these forms limestone pillars or columns. As the land surface is 
eroded, the roofs of such caverns fall in, and the underground streams become 
surface streams. Occasionally, however, a part of the roof remains, thus form- 
ing what are called natural bridges. The Xatural Bridge in Virginia is an example. 

88. Corrasion is a term proposed by Russel for the cutting and 
consequent deepening and broadening of a stream channel by the 
material produced by weathering, etc., as it is carried or transported 
by the running water from a higher to a lower level. This action 
is called by some erosion, thus limiting it to the mechanical action 
of the running water, but erosion, strictly speaking, includes 
weathering, transportation, and corrasion. 

When the materials derived from weathering, etc., are thrown 
into a running stream, its wearing and cutting power are greatly 
increased by its load of mineral matter ; {. e., the silt, sand, gravel, 
boulders, etc., that are carried from place to place by the moving 
waters. The amount of the corrasion is dependent both on the 
character of the transported materials and on their density. Other 
things remaining the same, the corrasion of a stream will depend 
on the inclination of its channel and on the volume of its running 
water. A stream may both deepen its channel by vertical corrasion, 
and broaden it by lateral corrasion. 

A most remarkable instance of erosion, due both to marked cor- 
rasion, and to the weathering of the banks above the water level, is 
seen in the canons of the Colorado River, where the waters have 
eaten a channel through the hard limestones and granites that form 
the bed of the stream, until they now run through gorges whose 
walls ascend almost perpendicularly to the height of from 3000 to 
6000 feet. 

A good idea of this great depth may be obtained by walking along a straight 
street for about a mile (5280 feet), and then imagining the street set upright in 
the air. On looking down toward the starting-place, we would see it as it would 
appear at the bottom of a hole about 6000 feet deep. 

When fragments of hard rocks are caught in eddies or whirls in 
rocky beds, the corrasion results in the formation of elongated or 



76 PHYSICAL GEOGRAPHY. 

pot-shaped holes, with smooth, steep sides and rounded bottoms, 
called, from their resemblance to ordinary iron pots, pot-holes. 

89. "Wind Corrasion and Transportation, sometimes called 
Wind Erosion. — It is not only moving water that corrades rocks. 
Bare rocky surfaces are worn away by strong winds, aided by the 
sharp particles of sand and other hard substances they carry with 
them. 

In some instances winds possess considerable power in transport- 
ing weathered and corraded materials when in the form of fine par- 
ticles or sand. On the borders of the Nile, in Egypt, the winds 
carry the sands of the desert and spread them over the narrow 
strips of fertile land bordering the river. Along many sea-coasts 
the winds are heaping up the sand in huge mounds called dunes or 
sand-hills. In Wyoming, on both sides of the Niobrara River, the 
wind has heaped up the sand over an area of about 20,000 square 
miles, thus forming a sandy desert. The sand is heaped up in round 
dome-shaped hills, the tops of some of which have been moulded by 
the whirling winds into shapes resembling craters. 

90. Avalanches and Land-slides. — The action of weathering 
is most marked on bare, rocky surfaces. Any cause, therefore, 
which tends to keep the surface bare, or which furnishes fresh sur- 
face to the action of the air, necessarily increases the rapidity of 
weathering. For example, the percolating waters may slowly under- 
mine or soften some of the deeper strata on the side of a mountain, 
thus causing the slipping of huge masses down the mountain, in 
what are called avalanches or land-slides. In this way the cutting 
down of the mountain is greatly accelerated. 

Weathering is more rapid in some kinds of rock than in others. Thus gran- 
ite, which consists of a mixture of felspar, mica, and quartz, is, in some varieties, 
readily broken up into a gravelly soil, owing to the comparatively rapid weather- 
ing of the felspar. 

91. Transportation and Deposition. — The fine broken rock 
produced by the action of weathering is called rock waste, and con- 
stitutes the material from which soil is formed. Rock waste seldom 
remains in place over the rock surface from which it was derived. 



DISTRIBUTION OF THE LAND-AREAS. 



77 



By the continued action of the wind, and of running water, it is 
gradually carried either to lower levels or to the ocean, where it is 
deposited. The process by which it is carried from a higher to a 
lower level is called transportation. By the action of transportation 
lower river valleys are filled with materials obtained from higher re- 
gions, the beds of lakes are gradually filled with sediment, and sand- 
bars are formed along sea-coasts. Deposits so formed are apt to again 
be carried or re-transported to lower levels, where they are re-deposited. 

92. The Action of Ocean Waves, changing the outlines of 
coasts ; as may be seen in portions of the coasts of England and 
Scotland. 

93. The Agency of Man is witnessed mainly in the destruction 
of the forests over extended areas. 



oj«io 



CHAPTER II. 



Distribution of the Land- Areas. 

94. Geographic Effects of Light, Heat, and Moisture. — The 
peculiarities observed in the distribution of animal and vegetable 
life are caused largely by differences 
in the distribution of light, heat, and 
moisture. Since light, heat, and moist- 
ure are influenced by the interaction 
of land, water, and air, we must first 
study the distribution and grouping of 
these inorganic or dead forms before we 
can understand those that are living. 

95. The Distribution of the Land. 
—Of the approximately 197,000,000 
square miles that make up the 
earth's surface, about 144,000,000 
are water and 53,000,000 land. The 
proportion is about as the square of 5 is to the square of 3. If, 




Fig. 



32. — Relative Land- 
Water-Areas. 



and 



78 PHYSICAL GEOGRAPHY. 

therefore, we erect a square on a side of five, its entire area will 
represent the relative water-area of the globe ; while a square whose 
side is three will represent the relative land-area. 

96. The Distribution of the Land may be arranged under two 
heads : 

(1) The Horizontal Forms of the Land, or the different shapes 
produced in the land-areas at the coast lines, by the contact of land 
and water ; 

(2) The Vertical Forms of the Land, produced by the irregularities 
of the surface of the high lands and low lands. 

97. The Horizontal Forms. — The land-areas are divided into 
continents and islands. 

The Eastern Hemisphere contains four continents : Europe, Asia, 
Africa, and Australia. The first three form one single mass, which 
is called the Eastern Continent. 

Though the word " continent " strictly refers to an extended area of land 
entirely surrounded by water, usage has sanctioned the application of the term 
to each of the grand divisions of the land. It is quite correct, therefore, to speak 
of the North American Continent, the Asiatic Continent, etc. 

The Western Hemisphere contains two continents: !North and South 
America ; these constitute what is called the Western Continent 
The following are the extremities of the continents : 

In the Eastern Continent — 

Most northern point, Cape Chelyuskin, lat. 78° 16' N. 
Most southern point. Cape Agulhas, lat. 34° 51' S. 
Most eastern point, E '=t Cape, long. 170° W. 
Most western point. Cape Verd, long. 17° 34' W. 

In the Western Continent — 

Most northern jjoint, T' iut Barrow, lat. 72° N. 
Most southern point, Cape Froward, lat. 53° 53' S. 
Most eastern point, Cape Zt. Eoque, long. 35° W. 
Most western point, Cape Prince of Wales, long. 168° W. 

98. Peculiarities in the Distribution of the Land : 

(1) The continents extend farther to the north than to the south. 

(2) The land masses are crowded together near the north pole, which 
they surround in the shape of an irregular ring. 



DISTRIBUTION OF THE LAND-AREAS. 79 

(3) The three main southern projections of the land — South Amer- 
ica, Africa, and Australia — are separated from one another by 
extensive oceans. 

99. Land and Water Hemispheres. — The accumulation of 
the land in the north and its separation in the south lead to a 
curious result — nearly all ihe land is collected in one hemisphere, and 
nearly all the water in another hemisphere. 

If one point of a pair of compasses be placed on tlie north pole of a globe, and 
the other stretched out to reach to any point on the equator, they will describe 
on the surface of the globe a great circle, and consequently will divide the globe 
into hemispheres. If, while they are stretched this distance apart, one of the 
points be placed at about the city of London, a circle swept with the other point 
will divide the earth into land and v/ater hemispheres. Such a great circle 
would pass through the Malay Peninsula and the coast of Peru. 

The Land Hemisphere contains all of North America, Europe, 
and Africa, and the greater part of South America and Asia. The 




Fig. 33.— Land and Water Hemispheres. 

Water Hemisphere contains the southern portions of South Amer- 
ica, the Malay Peninsula, and Australia. 

100. Double Continents. — The six grand divisions or conti^ 
nents may be divided into three pairs, called Double or Twin 
Continents. 

Each Double Continent consists of a northern and soi;thern con- 
tinent, almost separated from each other, but connected by a narrow 
isthmus or island chain. 

The three double continents are North and South America, 



80 PHYSICAL GEOGRAPHY. 

Europe and Africa, and Asia and Australia. There are, therefore, 
three northern and three southern continents. 

The northern continents lie almost entirely in temperate lati- 
tudes, while the southern lie mainly in the tropics. 

101. Lines of Trend, — The study of any Mercator's projection 
will disclose the following peculiarities in the earth's outlines : 

There are two great systems of trends, or lines of direction, along 
which the shores of the continents, the mountain-ranges, the oceanic 
basins, and the island chains usually extend. These trends are 
Dorth- easterly and north-westerly, and intersect each other at nearly 
right angles. There are, however, some wide deviations from these 
directions. 

North-East Trends. — A straight ruler may be so placed along the south- 
eastern coast of Greenland and the south-eastern coast of North America that 
its edge will touch most of their shore lines. Its general direction will be 
norfh-east. 

It may be similarly placed along the south-eastern coast of South America, the 
north-western coast of Africa, and most of the western coast of Europe ; along 
the south-eastern coast of Africa; the south-eastern coast of Hindoostan; and 
along the eastern coast of Asia, without its general direction differing much 
from north-east. 

North- West Trends. — A straight ruler may be so placed as to touch most 
of the western shores of North America and part of the western coast of South 
America; most of the western coast of Greenland, or the north-eastern coast 
of North America, and part of the western coast of Africa. All these courses 
are sensibly north-west. 

If placed with one end at the mouth of the Mackenzie Eiver, and the other 
on the south-western extremity of Lake Michigan, it will cut nearly all the 
great lakes in Central British America. The direction of the island chains of 
the Pacific Ocean is plainly characterized by these two trends, many of the sepa- 
rate islands being elongated in the direction of the trend of their chain. 

102. Continental Contrasts. — The main prolongation of the 
Western Continent extends in the line of the north-western trend, 
while that of the Eastern Continent extends in the line of the 
north-eastern trend. The axes of the continents, or their lines 
of general direction, therefore, intersect each other nearly at right 
angles. 

The Western Continent extends for considerable distances both 



DISTRIBUTION OF THE LANB-AREAS. 81 

north and south of the equator, while the Eastern Continent lies 
mainly north of the equator. The Western Continent, therefore, is 
characterized by a diversity of climates ; the Eastern Continent, by 
a similarity. The distribution of vegetable and animal life in each 
continent is necessarily affected by the peculiarities of its climate. 

103. Shore Lines. — When land bordering on the ocean is up- 
lifted, the part of the sea bottom which is raised above the water 
level forms a coast plain, whose shore lines are comparatively smooth 
or unbroken. The water near the coast is fairly shallow, and har- 
bors are few. But, when a subsidence occurs, the low land is covered 
by the water, until the mountains or highlands face the coasts. The 
shore lines are then irregular and complicated, the water near the 
coast is deep, and harbors are more numerous. 

All shore lines are subject to changes in outline by subsequent 
elevations or subsidences. Shore lines are also subject to changes 
by the action of the waves, ocean currents, or rivers. For example, 
sand-bars or reefs may form off shore, shutting off long, narrow 
bodies of water, called lagoons. The winds blow sand from the 
beach, and form huge irregularly shaped sand-drifts or dunes. More- 
over, the rivers and tidal currents still further modify the sand-bars 
by cutting them away in some places and re-depositing them in 
other places ; or, the rivers alone, deposit vast quantities of min- 
eral matter, either at their mouths or along the adjoining coast. 
Where the sea encroaches on the land the coastal plain may be 
cut back, thus forming a high bluff or cliff, washed by the sea at 
high tides. 

104. Changes in the Outlines of the Continents. — The grad- 
ual elevations and subsidences that are taking place in the earth's 
crust, whereby parts of the coast lines are submerged, or parts of 
the floor of the ocean sufficiently raised to become dry land, are 
causing changes in the continental outlines. These changes, how- 
ever, are so small in amount that they require long periods of time 
to become noticeable. 

The coast or shore lines of the northern continents are very irreg- 
ular, the shores being deeply indented with gulfs and bays, while 

6 



82 



PHYSICAL GEOGRAPHY. 



those of the southern continents are comparatively simple and 
unbroken. 

The continents are most deeply indented near the regions where 
the pairs of northern and southern continents are nearly separated 
from each other. 

The continents differ greatly from one another in the extent of 
their indentations. Europe is the most indented of all the conti- 
nents. The area of her peninsulas, compared with that of her 
entire area, is as 1 to 4. Asia comes next in this respect, the pro- 
portion being 1 to 5i, while in North America it is but 1 to 14. 

The following table gives, in the first column, the area of each of the conti- 
nents ; in the second, the length of coast line ; and in the third, the number of 
square miles of area to one mile of coast line : 









Square miles of 


Continents. 


Area. 


Coast line. 


surface for one 
mile of coast. 


Asia 


17,500,000 sq. miles. 


35,000 miles. 


500 


Africa 


12,000,000 " 


16,000 " 


750 


North America . 


8,400,000 " 


22,800 " 


368 


South America . 


6,500,000 " 


14,500 " 


449 


Europe .... 


3,700,000 " 


19,500 " 


190 


Australia .... 


3,000,000 " 


10,000 " 


300 



Europe has, in proportion to its area. 

About three times as much coast line as Asia. 
About four times as much as Africa. 
About twice as much as North America. 
More than twice as much as South America. 

Europe therefore is the most, and Africa the least, deeply indented 
of the continents. 

The extent and character of the coast line of a country has a 
marked influence on its progress in civilization. When harbors are 
numerous and safe, and water communication is possible with the 
interior of the continent, as in Europe and North America, progress 
is marked, but where the continent is shut in, has few harbors, and 
comparatively limited water communication, as in Africa and Aus- 
tralia, progress is restricted. 



DISTRIBUTION OF LAND-AREAS. 82a 

Modifications of Shore Lines.-Harbors.-A harbor is primarily a place 
of shelter from storms. A good harbor must be deep enough for large vessels 
must be connected with tiie open sea by a deep channel, and must provide room 
for many ships. The direction whence the storm waves come and the direction 
which the harbor entrance taces have much to do with its safety. Harbors may 
be classified as : 

(1) River harbors.— These are likely to have easy communication with the in- 
terior through river navigation, especially when at the mouth of rivers whose 
valleys are natural routes for railways. Their disadvantages are that the current 
is a handicap for coastwise sailing vessels, their moutlis may be blocked by mud 
and silt, and shallow water is common near the entrances. 

(2) Delta harbors.— In the delta of a large river there is usually one distribu- 
tary channel which is deep enough for ocean vessels, and on this a seaport is apt 
to be located. ISlew Orleans and Calcutta are examples. 

(3) Estuary harbors.— Most of the important harbors of the world have been 
made by the drownmg of river valleys. The harbors of New York, London, and 
Hamburg belong to this class. The advantages are that the entrance rarely 
shifts, it is likely to be deep, and often tidal currents keep it clear of sediment. 
Navigation may be possible for some distance inland. 

(4) Fiord harbors are excellent as far as depth of water, clear entrance, and 
complete protection are concerned, but they are seldom favorable for ports on 
account of high, steep shores, and inaccessibility from the land. Christiania and 
Glasgow are examples. 

(5) Lagoon harbors may be produced by the formation of sand bars, or by the 
growth of coral reefs. The water off shore is rarely deep, most of the inlets are 
narrow and shallow, and many have such strong tidal currents as to prevent the 
passage of small craft. The bordering lands are low and marshy, the island on 
the ocean side is low and sandy, and neither is fitted to be the site of a great port. 
Galveston is the best example. Lagoon harbors are due also to the formation of 
sand spits, atolls, rudely circular reefs enclosing a central lagoon, and to the 
presence of the craters of old volcanoes. These harbors are numerous in the 
South Pacific, but are of little commercial importance. 

Shore lines are also modified by plant and animal life. Mangrove trees in 
tropical regions, marsh and eel grass in other localities tend to hold soil on reefs 
and aid their growth into ofishore islands. The next chapter will show how 
marine animal life helps in this work. 

Lake shore lines are miniatures of ocean shore lines. The movements of the 
water produce a characteristic series of coast forms. Waves build up sand 
beaches behind which there is generally a lagoon. Barrier beaches and bay 
bars are formed. Where the coast land is high and the coast waters deep, the 
waves pound against the shore with tremendous force and undercut it into a 
vertical cliff, as along the shores of Lake Erie. 

Regular Shore Lines. — We have seen on page 81 that regular shore lines 
result from the migration of the shore line seaward due to the movement of the 



82b 



PHYSICAL GEOGRAPHY. 



earth's crust. Again the shore line may be extended seaward by the action of 
the ocean in building up sand reefs parallel to the shore and in filling up lagoons 
and inlets with sand. Cusp and crescent outlines are formed in this way. The 
cusp is an angular projecting beach or portion of a beach, formed by the inter- 
action of conflicting outlines. The shore line may migrate seaward by the 
formation of deltas at river mouths. A regular sliore line may result from the 




Fig. 33a.— The Sea at Work Smoothiug a Shore Line. 



smoothing action of waves and currents which produce sea cliffs, bay-head and 
barrier beaches, and land-tied islands like the Rock of Gibraltar. In high lati- 
tudes glaciers frequently carry down amass of debris which is deposited at bay- 
heads ; again, the action of the ice tends to smooth coast lines. 

Irregular Shore Lines. — The submergence of a coast land having hills and 
valleys produces a new shore line which is irregular, the drowned valleys form- 
ing bays. Isolated hills on the old lowlands may front the new coast as islands. 
The coast of Maine furnishes good examples. Commerce is favored by such 
a coast. 



ISLANDS. 83 

CHAPTER III. 
Islands. 

105. Relative Continental and Insular Areas. — Of the 
53,000,000 square miles of laud, nearly 3,000,000, or about one- 
seventeenth, is composed of islands. 

106. Varieties of Islands. — As regards their situation, islands 
are either continental or oceanic. 

Continental Islands are those that lie near the shores of the 
continents. They rest on shallow ocean beds, called continental 
shelves, that lie near the continents and that form parts of the 
submerged continents. Continental islands are, therefore, to be 
regarded as projections of the submerged continents. They have, 
usually, the same trends as the shores of the neighboring main- 
land. The British Isles and the Asiatic and Australian Island 
chains rest on the continental shelves of their adjoining continents. 

Continental islands, as a rule, are larger than oceanic islands ; this is caused 
by the shallower water in which they are situated. Papua and Borneo have 
each an area of about 250,000 square miles ; either of these islands is more than 
twice as large as the combined areas of Great Britain and Ireland. 

Many of the smaller continental islands, such as the numerous 
fiord islands off the coasts of Norway, British Columbia, Patagonia, 
and Maine ; the delta islands so common at the mouths of certain 
rivers ; the low sand-bars and mud fiat islands of certain coasts, and 
the small, high, rocky islands of other coasts, are of comparatively 
recent formation. 

107. American Continental Island Chains. 

(1) The Arctic Archipelago comprises the large group of 
islands north of the Dominion of Canada. It consists of detached 
portions of the neighboring continent. 

(2) The Islands in the Gulf of St. Lawrence and its neigh- 
borhood are apparently the northern prolongations of the Appala- 
chian mountain-system. They rest on or near the North American 
continental shelf. 



84 



PHYSICAL GEOGRAPHY. 




(3) The Bahamas lie off the south-eastern coast of Florida, to 
which they belong by position and structure. Their general trend 
is north-west. 

(4) The West Indies form a curved range, which connects the 
peninsula of Yucatan with the coast-mountains of Venezuela. 

Here both trends appear, 
though the north-western pre- 
dominates. They rest on or 
near the continental shelves 
of the two continents. 

(5) The Aleutian Islands 
form another curved range, 
which connects the Alaskan 
Peninsula with Kamtchatka; 
their general trend is north- 
east. They are connected 
with the elevations of the 
North American Continent. 

(6) The Islands "West of the Dominion of Canada and 
Alaska. — These are fiord islands, and are the summits of sub- 
merged northern prolongations of the Pacific coast ranges. 

(7) The Islands of the Patagonian Archipelago are also fiord 
islands or the summits of submerged prolongations of the Andes of 
Chili. 

108. Asiatic Continental Island Chains consist of a series of 
curved ranges extending along the coast, and resting on or near the 
Asiatic continental shelf. They intersect each other nearly at right 
angles. 

(1) The Eurile Islands are a prolongation of the Kamtchatkan 
range. 

(2) The Islands of Japan extend in a curve from Saghalien to 
Corea. 

(3) The Loo Choo Islands extend in a curve from the islands 
of Japan to the island of Formosa. 

(4) The Philippines form two diverging chains, which merge on 



Fig. 34.— West India Island Chain. 

1, Cuba ; 2, Hayti ; 3, Jamaica ; 4, Porto Rico ; 
5, Caribbee Islands ; 6, Bahamas. 



ISLANDS. 



85 



the south into the Australasian Island chain. The eastern chain 
extends to the southern extremity of Celebes, and the ■western to 
that of Borneo. 

The Asiatic chains belong to a submerged mountain-range extending from 
Kamtchatka to the Sunda Islands. Their general direction is parallel to the 
elevations of the coast. 

109. The Australasian Island Chain, 

The Australasian Island chain is composed of a number of islands 
extending along curved trends over a length of nearly 6000 miles, 
from Sumatra to New Zea- 
land. They rest on or near 
the Asiatic or Australasian 
continental shelves. The 
islands extend along three 
curved lines, whose general 
direction is north-west. 

The Australasian chain was prob- 
ably connected with the Asiatic Con- 
tinent during recent geological time, 
and separated from it by subsidence. 
Its numerous volcanoes and coral 
formations prove that subsidence 
is still taking place. 

110. Peculiarity of Dis- 
tribution. — The following 
peculiarity is noticed in the 
distribution of continental 
islands : 

Each of the continents has an island, or a group of islands, near its 
south-eastern extremity. For example, North America has the 
Bahamas and the West Indies ; Greenland has Iceland ; South 
America has the Falkland Islands ; Africa has Madagascar ; Asia 
has the East Indies ; and Australia has Tasmania. 

111. Oceanic Islands are those situated far away from the con- 
tinents. They occur either in vast chains, which generally extend 
along one or the other of the two lines of trend, or as isolated groups. 



"l ^ V 






\^ A^ 


ti 






14 


15 


2 3 4fi^ 


'~1 /v •■^« 


• . 16 




^\ 11' 


V 

c V17 


AUSTRALIA "N 


i> 


w 


A7 


/ 



Fig. 35.— Australasian Island Chain. 

1, Sumatra ; 2, Java ; 3, Sumbawa ; 4, Flores ; 
5, Timor; 6, Borneo; 7, Celebes; 8, Gilolo; 9, 
Ceram; 10, Papua; 11, Louisiade Archipelago; 
12, New Caledonia ; 13, New Zealand ; 14, Ad- 
miralty Islands; 15, Solomon's Archipelago; 
16, Santa Cruz ; 17, New Hebrides. 



86 



PHYSICAL GEOGRAPHY. 



Oceanic Island Chains. 

The following are the most important : 

(1) The Polynesian Chain ; 

(2) The Chain of the Sandwich Islands ; 

(3) The Tongan or New Zealand Chain. 

The Polynesian Chain consists of a series of parallel chains, 
extending: from the Paumotu and the Tahitian Islands to the Caro- 

lines, the Ralick, and the 
Radack groups. Their gen- 
eral direction is north-west ; 
the total length of the chain 
is about 5500 miles. 

The Chain of the Sand- 
wich Islands extends in a 
north-westerly direction. Its 
length is about 2000 miles. 

The New Zealand Chain 
extends north-east as far as 
the Tonga Islands, cutting 
the Australasian chain at 
right angles. 

112. Isolated Oceanic 
Islands are mainly of tAvo 
kinds : the Volcanic and the Coral. As a rule, the Volcanic islands 
are high, while the Coral islands seldom rise more than twelve feet 
above the water. 

Volcanic Islands are not confined to isolated groups, but occur 
also in long chains. The Polynesian, Sandwich, and New Zealand 
Chains contain numerous volcanic peaks. But the high, isolated 
oceanic islands are almost always of volcanic origin, and, consisting 
of the summits of submarine volcanoes, are usually small. Some 
of the Canary and Sandwich Islands, which are of this class, rise 
nearly 14,000 feet above the sea. 

113. Coral Islands, or Atolls, though of a great variety of 
shapes, agree in one particular : 





^-., 




•■. \\iiX 


13^^~V 




■■^--j^x 


\. 


•• 


8*' 




1^ 



Fig. 36. — Polynesian Island Chain. 

1, Marquesas; 2, Paumotu; 3, Tahitian; 4, 
Rurutu group ; 5, Hervey group ; 6, Samoan, or 
Navigator's ; 7, Vakaafo group ; 8, Vaitupu ; 9, 
Kingsmill; 10, Ralick; 11, Radack; 12, Caro- 
lines; 13, Sandwich. 



ISLANDS. 



87 



They consist of a low, narrow rim of coral rock, enclosing a body 
of water called a lagoon. 





Fig. 38.— Coral. 



Fig. 37.— A Coral Island. 

114. Mode of Formation of Coral Islands. — The reef form- 
ing the island is of limestone, derived from countless skeletons of 
minute polyps that once lived beneath the 
surface of the waters. The skeletons, how- 
ever, are not separate. The polyp propagates 
its species by a kind of budding ; that is, a 
new polyp grows out of the body of the old. 
In this way the skeletons of countless millions 
of polyps are united in one mass, and assume 
a great variety of shapes. 

One of the most common species of reef-forming 
corals, the madrepora, is shown in Fig. 38. Many 
other forms exist. 

The delicate coral structures, together with 
shells from mollusks and calcareous plants, are ground into frag- 
ments by the action of the waves ; by the infiltration of water con- 
taining lime in solution, they become compacted into hard lime- 
stone, on which new coral formations grow. 

The growth of the coral mass is directed upward, and ceases when low-water 
mark is reached, because exposure to a tropical sun kills the polyps. But the 
action of the waves continues, and the broken fragments are gradually thrown 
up above the general level of the water. In this way a reef is formed, whose 
height, limited by the force of the waves, seldom exceeds twelve feet. 

On the bare rock, which has thus emerged, a soil is soon formed and a scanty 
vegetation appears, planted by the hardy seeds scattered over it by the winds 
and waves. 

The coral island never affords a very comfortable residence for man. The 
palm tree is almost the only valuable vegetable species ; the animals are few and 
small, and the arable soil is limited. Moreover, the island is subject to occa- 
sional inundations by huge waves from the ocean. 



88 PHYSICAL GEOGRAPHY. 

115. Distribution of Coral Islands. — According to Dana, the 
reef-forming coral polyp is found only in regions where the winter 
temperature of the waters is never lower than 68° Fahr. Some 
varieties, however, will grow in colder water. Coral islands are 
confined to tropical waters where the depth does not greatly exceed 
100 feet, and which are protected from cold ocean-currents, from 
the influence of fresh river waters, and from muddy bottoms; and 
which are remote from active volcanoes, whose occasional submarine 
action causes the death of the coral polyp. Though some coral 
polyps grow in quiet water, the greater part thrive best when 
exposed to the breakers. The growth, therefore, is more rapid on 
the side toward the ocean than on the side toward the island. 

Coral islands are most abundant in the Pacific Ocean. The following groups 
contain numerous coral islands : the Paumotus, the Carolines, the Eadack, the 
Ealick, the Kingsmill groups, the Tahitian, Samoan, and Fijii Islands, and New 
Caledonia. In the Indian Ocean are the Laccadives and the Maldives, and in 
the Atlantic Ocean, the West Indies and the Bermudas. 

116. Varieties of Coral Formations. — There are four varieties 
of coral formations : 

(1) Fringing- Reefs, or narrow ribbons of coral rock, lying near 
the shore of an ordinary island. 

(2) Barrier Reefs, which are broader than Fringing Reefs, and 
lie at a greater distance from the shore, but do not extend entirely 
around the island. 

A barrier reef oflf the coast of New Caledonia has a length of 400 miles. One 
extends along the north-eastern shore of Australia for over 1000 miles. Barrier 
reefs are not continuous, but often have breaks in them through which vessels 
can readily pass. 

(3) Encircling Reefs are barrier reefs extending entirely around 
the island. As a rule, encircling reefs are farther from the shore 
of the island than barrier reefs. Tahiti, of the Society Islands, is 
an example of aVi encircling reef. 

(4) Atolls. — This name is given to reefs that encircle lagoons 
or bodies of water entirely free from islands. 

The varieties of reefs just enumerated mark four successive steps 
or stages in the progress of formation of the coral island. 



ISLANDS. 



89 



When a more careful study of the habits of the reef-forming coral polyp disclosed 
its inability to live in the ocean at greater depths than 100 or 120 feet, the opinion, 
which formerly prevailed, of coral islands rising from profound depths, had to 
be abandoned. This belief had its foundation in the fact that a sounding-line 
almost invariably showed depths of thousands of feet of water near the shore of 
a coral island, and yet brought up coral rock. In no case, however, did the rock 
contain living polyps. A hypothesis of Darwin, which appears weU sustained 
by the extensive observations of Dana and others, explains the great depth of 
coral formations. 

117. Darmn's Hypothesis of Coral Islands. — According to this 
naturalist, the coral formation begins near the shore of an island 
that is slowly sinking. If the growth of the reef upward equals the 
sinking of the island, the thickness of the reef is limited only by the 
time during which the operation continues. 

In Fig. 39 is shown, in plan and section, an island with elevations, A and B, 
and river, a. The coral island begins as a fringing reef, somewhere off the coast 
of an ordinary island at c, c, c, when the 



"^-.. 




conditions are favorable. The coral reef 
must gradually extend around the island, 
since its growth toward the ocean is soon 
limited by the increasing depth, and 
toward the shore of the island, by the 
muddy waters near the surf and the 
absence of the breakers. 

Meanwhile, as the island is sinking, 
the channel separating the reef from the 
coast increases in breadth. A harrier 
reef is thus formed, which at last com- 
pletely surrounds the island, and becomes 
an encircling reef. The higher portions 
of land, which are still above the waters, 
form islands in the central lagoon. Op- 
posite the mouth of the river a, the 
growth is prevented by the fresh water, 
and a break in the reef is thus produced. 
These breaks are sometimes suflSlcient to 
permit a ship to enter the lagoon. At last all traces of the old island disappear, 
and its situation is marked by a clear lagoon, surrounded by a narrow rim of coral 
which follows, approximately, the old coast line. 

Parts of the coral region of the Pacific appear to have ceased subsiding, as tht 
wooded condition of the islands shows. In some cases subsequent elevation haa 
occurred. 




Fig. 39.— Growth of a Coral Island. 



90 



PHYSICAL GEOGRAPHY. 



118. Other Hypotheses of Coral Formations. — Recent obser- 
vations sliow that thie formation of some coral reefs, especially of 
many that lie along the continental shores, cannot be explained by 
Darwin's hypothesis. For example, Louis Agassiz has shown that 
the southern part of Florida is of coral formation, and has been 
deposited by means of successive concentric barrier reefs, that have 
been converted into continuous land by the accumulation of sand 
aud silt between adjoining reefs. LeConte similarly attributes this 
Florida formation to the deposit of a submarine shell bank, by the 
action of the Gulf Stream. When the bank was sufficiently near 
the surface, the coral polyps began to grow, especially near the edge 
where the food supply was sufficient. Alexander Agassiz has pro- 
posed a similar hypothesis, but regards the Gulf Stream as bringing 
food for the coral polyps rather than shells, sand, and silt for the 
formation of submarine flats. 



Figure 40 is a map of Florida with its reefs and keys. Figure 41 is a sec- 
tion along the line A-A. In Figure 40 the line a, a, shows what was at one 

time the limit of the southern coast 
of Florida, b, b, b, b, is the present 
limit of the southern coast, c, c, c, c, 
are the keys, which are low islands. 
d, d, is the growing coral reef, e, c, are 
the Everglades, dotted with islands, 
called hummocks. Between c, c, and 
d, d, is the ship channel. Outside the 
growing coral reef d, d, are the pro- 
found depths of the Gulf Stream, G. S. 
The growth of the reef-formations 
is explained by LeConte as follows 
(Fig. 41) : a was at one time the limit 
of the southern coast of Florida. 6 is 
the present southern coast, which at 
one time was a coral reef like d. Upon 
6, a line of coral islands gradually 
formed, connecting it with the old 
southern coast, a. The ship channel 
between a and b gradually filled up 
and formed the Everglades e, e. Mean- 
wMle, another reef formed in the position of the present keys c, the ship channel 




G.J^? 



Fig. 40.— Florida Reefs and Keys 
(LeConte). 




G.S. 



RELIEF FORMS OF THE LAND. 91 

being between 6 and c. This reef bas now grown to be a line of coral islands, 

and the ship channel, between h and c, converted into shoals and mud flats /• 

The present ship channel is be- 

tweeh c and d. In course of 

time the southern coast will 

extend to the present line of 

keys c, and the shoal water /, 

will become another Everglades. 

Outside the present keys c, an- \ \ ^= 

other coral reef d, is growing, to \ • \ , ^ 

which the coast will ultimately \ \ 

extend, and which will mark p^g 41.-Everglades, Reefs, aJid Keys of 

the limit of the formation, owing Florida (LeConte) . 

to the deep waters of the Gulf 

Stream, immediately beyond it. The dotted lines show the successive steps of its 

formation. 

Murray proposes a similar hypothesis, which he endeavors to apply to all 
coral formations. He supposes the accumulation of shallow shell and sand banks, 
and the growth thereon of the coral polyps, where the water is not too deep. 
Growth is limited to the edge of the banks, where the food supply is sufiiciently 
great, thus leaving the central lagoon. According to this hypothesis, coral for- 
mation would afford an evidence of rest, or even of elevation, rather than of subsi- 
dence. This hypothesis does not appear to be able to explain the formation of 
the numerous coral islands of the Pacific and the deep ocean generally. For 
these, Darwin's hypothesis is almost universally adopted. But that views simi- 
lar to those outlined by the Agassizs, LeConte, Murray, and others, account 
for the formation of Florida, the reefs of Yucatan, the Bahamas, the sunken 
coasts of Cuba, the coasts of Brazil, and possibly the coast of Australia is now 
generally credited. 

CHAPTER IV. 

Relief Forms of the Land. 

119. By the Forms of Relief of the Land is meant the eleva= 
tion of the land above the mean level of the sea. 

The highest land in the world is Mount Everest, of the Himalayas; 
it is 29,000 feet above the level of the sea. The greatest depression 
is the Dead Sea in Palestine, which is about 1312 feet below the 
level of the sea. The sum of these is somewhat less than six miles. 

An elevation of six miles is insignificant when compared with the 



92 



PHYSICAL GEOGRAPHY. 



-r 4000 miles. 



size of the earth. If represented on an ordinary terrestrial globe, 
it would be scarcely discernible, since it would project above the 
surface only about the YsVoth of the diameter. The highest eleva- 
tions of the earth are proportionally much smaller than the wrinkles 
on the skin of an orange. 

If, as in Fig. 42, a sphere be drawn to represent the size of the erjth, its radius 
will be equal to about 4000 miles. If, now, the line A B, be drawn equal to the 

radius, it will represent a height of 4000 miles. 
One-half this height would be 2000 miles ; one- 
half of this 1000, and successive halves 500 and 
250 miles. An elevation of 250 miles would not, 
therefore, be very marked. 

Although the irregularities of the sur- 
face are comparatively insignificant, yet 
they powerfully afiect the distribution of 
heat and moisture, and, consequently, that 
of animal and vegetable life. An elevation 
of about 350 feet reduces the temperature 
of the air 1° Fahr. — an effect equal to a 
difference of about 70 miles of latitude. 
High mountains, therefore, though under 
the tropics, may support on their higher 
slopes a life similar to that of the temper- 
ate and the polar regions. 
120. The Relief Forms of the Land are divided into two classes : 
Low Lands and High Lands. — The dividing line between 
low lands and high lands is usually taken at 1000 feet, which is the 
mean or average elevation of the land. This distinction, however, 
is not always observed. 

Low Lands are divided into plains and hills. 
High Lands are divided into plateaus and mountains. 
If the surface is comparatively flat or level, it is called a plain 
when its elevation above the sea is less than 1000 feet, and a plateau 
when its elevation is 1000 feet, or over. Even an irregular, hilly 
surface, when extensive, is sometimes, though inaccurately, called a 
plateau, even when considerably under 1000 feet in elevation. 




Fig. 42. 



—Relative Height of 
Mountains. 



RELIEF FORMS OF THE LAND. 



93 



If the surface is diversified, the elevations are called hills when 
less than 1000 feet high; and mountains when 1000 feet or over. 

The low lands of the Eastern Continent lie mainly in the northern 
part ; those of the Western Continent lie mainly in the central parts. 

12lt Plains owe their comparatively level surface either to the 
long-continued erosion of high lands ; to the gradual settling of 
sedimentary matter, or to extended lava floods. 

122. Classes of Plains. — Plains are generally overspread with 
a deep layer of mantle rock brought down from higher land by 
streams, glaciers, and winds, or produced by the decay of the bed 
rock underneath. They may be classified as : 

(1) Coastal Plains. These are formed by the slow rising of the 
sea bottom until it emerges from the water. They are covered with 
sediment deposited off shore and are continuous with the submerged 
plain of the continental shelf. They are generally narrow, but 
sometimes they stretch 
back hundreds of miles 
to the plateau or moun- 
tains behind them. On 
the narrow plains the 
drainage systems are 
simple; on the broad 
plains systems of drain- 
age belts are developed. 
The sandy layers cf the 
Atlantic and Gulf coas- 
tal plains contain hun- 
dreds of artesian wells. 
A slight sinking of this 
plain has admitted the 
sea into the valleys, 
embaying the former marginal land. Ancient coastal plains some- 
times occur in the interior of continents, far from the sea. They 
were formed in the same way as the others, along the shore of a 
sea which has long since disappeared. Where the coastal plains 




Fig. 43.— Portion of Atlantic Coastal Plain. 



94 



PHYSICAL GEOGRAPHY. 



are broad, cities are situated both at the mouths of the larger rivers 
and at the head of navigation, that is, on the inner margin of the 
coastal plain, at the foot of the mountain ranges. Wilmington, 
Charleston, and Raleigh are examples. 

(2) Alluvial Plains. Plains made by the accumulation of river 
sediment are called alluvial. The alluvial plains of the Mississippi, 
the Amazon, and the Nile are among the largest in the world. A 

large river, more or less along its whole 
course, but especially toward its mouth, 
gets out of its banks in times of high wa- 
ter, spreads over the adjoining country, 
and deposits a coat of mud or sand, thus 
buildiug up a smooth surface known as 
a flood plain. (See pages 143-146 for 
a discussion of the work of rivers.) 

(3) Lacustrine Plains. — A lake 
basin may in time be filled up with 
the sediment which streams deposit in 
it and converted into an almost per- 
fectly level lake plain or lacustrine 
plain. The wheat district of Min- 
nesota, North Dakota, and Manitoba 
is the bed of an old glacial lake. 

(4) Glacial Plains. — In Europe 
and North America millions of square 
miles have been covered by continental 
ice sheets which deposited vast sheets 
of mantle rock or glacial drift, of such 
thickness as to fill up, bury, and 
smooth over the bed-rock surface. 

This nearly level surface is called a glacial plain. Lakes are gen- 
erally numerous on a glacial plain owing to its youth. 

(5) Plains of Denudation., or Peneplains. — Some large plains, 
once high and rough, have been worn down by weathering and the 
work of streams and slaciers to an even surface not far above sea 




Fig. 44. — River-made Plains 
of San Joaquin. 



RELIEF FORMS OF THE LAND. 



95 



level. These are generally studded with low, rounded hills, com- 
posed of materials less easily eroded than the rest. These are pene- 
plains, or plains of denudation. 

123. Classes of Plateaus. — Plateaus are divided into classes 
according to their position, as marginal, or those extending along 
the course of a mountain-chain, and intermont, or those which 
occupy a wide region between distant mountains. They may be 
divided, according to their age, into young and old plateaus. 

Young Plateaus, like young plains, owe their level surface to the 
horizontal strata which form them. They appear to have been 
deposited under the sea and to have been uplifted without much 
disturbance. 

Old Plateaus. — As the age of a plateau increases, the action of the 
rivers and weathering increases, and the plateau becomes more and 
more " dissected " until 
it may, at last, disap- 
pear, except that, here 
and there, portions of 
the old surface stand 
in bold relief on the 
low land as flat-topped 
table mountains, some- 
times called mesas, or 
buttes. 

Broken Plateaus are plateaus crossed by lines of fracture, called 
faults, which mark the boundary of differences in level. In a 
plateau of this type in Colorado and x4.rizona, the fault lines 
extend north and south. The differences in level amount to several 
thousand feet. 

124. Mountains. — In a mountain-range the (yrest or summit of the 
range separates into a number of detached portions called peaks; 
below the peaks the entire range is united in a solid mass. 

The breaks in the ridge, when extensive, form mountain-passes. 

The influence of inaccessible mountains, like the Pyrenees and the Himalayas, 
in preventing the intermingling of nations living on their opposite sides, is well 




Fig. 45.— A Butte in New Mexico. 



96 



PHYSICAL GEOGRAPHY. 



exemplified by liistory. In the past, mountains formed tlie boundaries of differ- 
ent races. Some mountains, like the Alps and the Appalachians, have numerous 
passes. 




Fig. 46.— Chilcoot Pass, British Columbia. 

A Mountain-System is a name given to several more or less con* 
nected ranges. Mountain-systems are often thousands of miles in 
length and hundreds of miles in breadth. 

The Axis of a Mountain-System is a line extending in the general 
trend of its chains. 

According to a recent terminology, a mountain-system is limited to the more or 
less independent ranges that have been thrown up, in a given region, during the 
same geological epoch. A mountain-chain is limited to a combination of mountain- 
systems of different epochs ; while the combination of several mountain-chains, 
that have been formed at different geological epochs, forms what is called a c(yr- 
dillera. A strict application of these terms, in discussing the mountains of the 
world, would not only necessitate a treatment of the subject in far greater detail 
than space permits, but would also require us to assign to mountains qualifying 
names that would not be generally recognized. We shall, therefore, adhere to 
the definitions which are preferred and used by the best authorities. 




RELIEF FORMS OF THE LAND. 96a 

125. Economic Importance of Plains and Plateaus — On 
account of their fertility, accessibility, and mild climate, plains 
have been the most densely populated regions of the earth. Allu- 
vial, glacial, and lacustrine plains, on account of depth and fertility 
of soil, are the best agricultural regions. About 70 per cent of the 
world's people live less than 1000 feet above sea level. The 
wealthiest and most progressive peoples and the great cities are 
found on the plains. Coastal plains are less productive than the 
others. Worn-down plains are often infertile, but sometimes 
support forests and are apt to be rich in minerals. 

Plateaus are less 
favorable for man 
on account of poorer 
soil, rougher surface, 
and colder and drier 
climate. Very high 

plateaus, such as Thi- ^. .„ „. „ „ 

7^ Fig. 46a.— Strata Bent Upward and Broken. Note 

bet, have an arctic cli- the Layer of Coal. 

mate and are almost 

uninhabitable. The tropical plateaus, such as those of Mexico, Peru, 

and Central Africa, have a temperate climate, and are better homes 

for men than the hot and unhealthful plains which border them. 

In middle latitudes, plateaus of moderate height, such as the Great 

Plains of the United States and some Central Asian plateaus, 

constitute a region of grassy stej)j)es, over which the people wander 

with their herds of horses, cattle, and sheep in search of pasture. 

126. Origin of Mountains. — -Mountains are unlike plateaus of 
similar elevation in having little stretch of surface at the top. They 
are conspicuously high lands which have but slight summit areas. 
Mountains appear to have their origin in the strain produced by the 
slow cooling of the interior of the earth, which, shrinking away 
from the crust, subjected the crust to enormous lateral pressures as 
it slowly accommodated itself to the new conditions. This crustal 
movement is called diastrophism. Many of the higher isolated 
mountains are volcanic cones. Many mountains have been formed 



96b 



PHYSICAL GEOGRAPHY. 




Fig. 46b Block Mountains Produced by Crustal Pressure. 




Fig. 46c.— Massive Mountain Formation Due to Volcanic Action. 



RELIEF FORMS OF THE LAND. 97 

by great intrusions of lava which have lifted the overlying beds 
high above the level of the surrounding country. This cause is called 
vulcanism. Erosion, or the gradual wearing away of the land up- 
lifted above sea level, explains the existence of many mountains. 
They have been left standing in bold reUef by the removal of the 
surrounding weaker rocks. Pike's Peak, the Colorado Eockies, and 
the Catskill Mountains of Kew York are due to unequal erosion. 

Classification of Mountains.— According to their origin 
mountains are classified as : 

(1) Block or Faulted Mountains. The great lateral pressures 
of the crust fractured, folded, 
or crushed the crust, causing 
it to subside or sink in certain 
places and to be elevated in 
others in a series of great 
blocks. Block mountains in 
various stages of dissection 
occur in Oregon, Nevada, and ^i&- 46d— strata Broken by Great 

1 , Pressure, 

elsewhere. 

(2) Folded Mountains. Some mountains consist of a series of folds 
formed by compression from the sides. In some cases the folds are 
open and regular ; in others they are closed, irregular, and over- 
turned. In some cases the strata of the folds are faulted, and some 
of the faults record a vertical displacement of thousands of feet. 
By the lateral pressure both anticlines, or arched upfolds of the 
strata, and synclines, or downfolds of the strata, are produced. 

(3) Massive Mountains. This name is applied to the mountains 
due to volcanic action or to the injection of lava between strata. 
The Henry Mountains of Utah and the Park and the Elk ranges in 
Colorado are examples. Mountains which are due to the resistance 
of their rocks belong to this type. 

127. Life History of Mountains. — When the strain becomes 
too great as the earth strata slowly bend, the rocks slip along fault 
planes. Through the deep fissures, lava may rise, building vol- 
canic cones. Immediately erosion attacks the young mountains. 



98 PHYSICAL GEOGRAPHY. 

Since they cannot be worn down as rapidly a& they are elevated, 
they continue to grow higher. Glaciers extend down the valleys. 
Broad valleys are formed by down-folding, and streams cut narrow 
gorges. Finally the uplift ceases, but erosion broadens the valleys 
and lowers the peaks. The glaciers disappear, the slopes are for- 
ested, the valleys are tilled. These mountains are called mature. 
Further lowering may continue until the mountains are reduced to 
low, rolling hills. The surface becomes a peneplain, and the moun- 
tains are called old. After being worn down, a mountain region 
may be again uplifted and made to start on a new life history, as 
has been the case with the Appalachians. Then erosion may etch 
the ridges of hard rock into relief again, and form broad valleys 
where the strata are weak. The height of mountains, then, is 
dependent on their initial elevation, the vigor of the agents of 
erosion, the resistance of the rocks, and the age of the mountains. 

128. Econoraic Relations of Mountains. — Mountains are 
barriers to the migration of plants, animals, and men. They are 
difficult to penetrate, to cross, or to live on. The vertical height 
and steepness render transportation costly and diflicult. They hin- 
der commercial relations. The Appalachians, the Alps, the Hima- 
layas, and the Pyrenees are types of these barriers. In addition 
they hinder or prevent the uniform distribution of temperature and 
rainfall by acting as condensers of water vapor ; they check the 
distribution of plants and animals so that often the conditions and 
inhabitants upon opposite sides of a mountain range are very 
unlike. The permanent population of mountains is sparse. The 
people are rude, hardy, and active, and luxuries are few. 

The climate of mountains is severe, and the higher summits are 
covered with snow and ice. The temperature decreases 1°, on the 
average, for every 300 feet of elevation. On high mountains there 
is a line, called the timber line, above which no trees can grow. 
The line above which there is perpetual snow is called the snozv line. 
Mountains in the path of vapor-bearing winds have abundant rain- 
fall on the slopes against which the winds blow. The opposite slopes 
are dry because so much vapor is lost in passing over the mountains. 



RELIEF FORMS OF THE LAND 99 

The climate, scenery, boating, fishing, and hunting attract people 
to the mountains for a vacation. The mountains of New England, 
the Adu'ondacks, the Catskills, and the Canadian Eockies are vis- 
ited each year by large numbers of people. The Alps are famous 
as health resorts and playgrounds and are visited by a million people 
every year. Mountains are important timber reserves^ because 
agriculture has not demanded the removal of the forests. The 
relation of mountain forests to the flow of streams rising in them, 
and to the problems of navigation, water power, irrigation, and 
soil erosion is very important. Many mountains contain valuable 
mineral deposits^ which attract settlers. Folding and erosion help 
to reveal these deposits. In the western United States gold, silver, 
lead, and copper are most important ; but zinc, iron, coal, and build- 
ing stones are also found. In the mountains of the eastern states 
coal, iron, and building stones are the leading mineral products. 

129. Valleys in mountainous regions are either longitudinal or 
transverse. 

Long-itudinal Valleys are those that extend in the direction of 
the length of the mountains. 

Transverse Valleys extend across the mountains. It is in trans 
verse valleys that most mountain passes occur. 

Although valleys, like mountains, initially owe their origin to the contraction 
of the cooling crust, yet their present shapes are, as a rule, profoundly modified 
by the action of other forces. Both in the longitudinal and transverse valleys, 
the rivers, by erosion, aided by the weathering of their slopes, either cut new 
courses or valleys, or deepen their old valleys in some places, and fill them 
in others. Extensive land-slides often alter the configuration of the river val- 
leys. During the glacial epoch many valleys were greatly changed by disturb- 
ances in their drainage due to damming up of the streams by large ice masses. 
Many fiord valleys were also formed by the eroding power of moving ice masses. 

1.30. Peculiarities of Continental Reliefs. — The following 
peculiarities are noticeable in the relief forms of the continents : 

(1) The coniinents have, in general, high borders and a low interior. 

(2) The highest harder lies nearest the deepest ocean; hence, the 
cidminating point, or the highest point of land, lies oid of the centre 
of the continent. 

(3) The greatest prolongation of a continent is always that of its 
predominant mouniain-system. 



100 PHYSICAL GEOGRAPHY. 

(4) The prevailing trends of the mountain-masses are the same as thos6 
of the coast lines, and are, in general, either north-east or north-west. 

lu describing the relief forms of the continents we shall observe 
the following order : 

(1) The Predominant System, or a system of elevations exceed- 
ing all others in height, and containing the culminating point of the 
continent. 

(2) The Secondary System or Systems, inferior to the pre- 
ceding in height. 

(8) The Great Low Plains. 

— ^>©^o« 



CHAPTER V. 

Relief Forms of the Continents. 

I. NORTH AMERICA. 

131. Surface Structure. — The Predominant Mountain-system 
lies in the west. 

The Secondary Systems lie in the east and north. 
The Great Low Plains lie in the centre. 

132. The Cordillera of the Rocky Mountains, the predomi- 
nant system, extends from the Arctic Ocean to the Isthmus of 
Panama. It consists of an immense plateau, from 300 to 600 
miles in breadth, crossed, from north to south, by two nearly par- 
allel mountain-ranges : the Rocky Mountains on the east, and the 
Sierra Nevada and Cascade ranges on the west. The eastern 
mountain-range is highest near the south ; the western range is 
highest near the north. Between these lie numerous parallel ranges 
enclosing longitudinal valleys, connected in places by transverse 
ranges forming basin-shaped valleys. 

The Rocky Mountains rise from a plateau whose elevation, in the 
widest part of the system, varies from 6000 to 7000 feet above the 
sea; therefore, although the highest peaks range from 11,000 to 
nearly 15,000 feet, their elevation above the general level of the 



BELIEF FORMS OF THE CONTINENTS. 



101 



plateau is comparatively inconsiderable. The plateau on the east 
rises by almost imperceptible slopes from the Mississippi River. 
The upper parts of the slopes, near the base of the mountains, form 
an elevated plateau called the " Plains," over which, at one time, 




Fig. 47.— OrograpMc Chart of North America. (Light portions, mountains; 
shaded portions, plains.) 
1, The Rocky Mountains ; 2, The Sierra Nevada and Cascade Ranges ; 3, Sierra 
Madre ; 4, Great Interior Plateau ; 5, Wahsatch Mountains ; 6, Appalachians ; 7, Plateau 
of Labrador ; 8, Height of Land ; 9, Arctic Plateau ; 10, Mackenzie River ; 11, Nelson 
River ; 12, St. Lawrence River ; 13, Mississippi River. 

roamed vast herds of buffalo or bison. This animal has practically 

become extinct, and has been replaced by domestic cattle. 

Though the name " Eocky Mountains " is usually confined to those parts of 
the chain vrhich extend through British America and the United States, yet, 
in connection with the Sierra Nevada Eange, it is continued through Mexico by 
the Sierra Madre Mountains, and by smaller ranges to the Isthmus of Panama. 

The Rocky Mountains form the great watershed of the continent; 



102 



PHYSICAL GEOGRAPHY. 




Fig. 48.— The Timber Line in the Canadian Kockies. 



the eastern slopes draining mainly through the Mississippi into the 
Atlantic, and the western slopes draining through the Columbia 

and the Colorado into 
the Pacific. The Rocky 
Mountains attain their 
greatest elevation in the 
volcanic peak of Popo- 
catepetl, 17,720 feet 
above the sea. 

The Sierra Nevada 
and Cascade Ranges 
extend, in general, par- 
allel to the Rocky 
Mountains. They take 
the name of Sierra 
Nevada in California 
and Nevada, and of 
the Cascade Mountains in the remaining portions of the continent. 
It reaches its greatest elevation in Mount McKinley, in Alaska, 
20,464 feet above the sea. This is the culminating 'point of the 
North American Continent. 

In the broadest part of the plateau of the Pacific system, between the Wah- 
satch Mountains on the east, and the Sierra Nevada and Cascade ranges on the 
west, lies the plateau of the Great Basin. Its high mountain borders rob the 
winds of their moisture, and the rainfall, except on the mountain-slopes, is incon- 
siderable. The Great Basin has a true inland drainage. 

The heights of all mountains, except those much frequented, must generally 
be regarded as approximations, since the methods employed for estimating 
heights require great precaution to secure trustworthy results. Even the cul- 
minating points of all the continents have not, as yet, been accurately ascertained. 

133. The Secondary Mountain-systems of North America 
comprise the Appalachian System, the Plateau of Labrador, the 
Height of Land, and the Arctic Plateau. The last three have but 
an inconsiderable elevation. 

The Appalachian Mountain-system consists of a number of nearly 
parallel chains extending from the St. Lawrence to Alabama and 
Georgia. It is high at the northern and southern ends, and slopes 



I 



RELIEF FORMS OF THE CONTINENTS. 103 

gradually toward the middle. The highest peaks at either end 

have an elevation of about 6000 feet. 

The Appalachian System is broken by two deep depressions, traversed by the 
Hudson and Mohawk Eivers. Between the foot of the system and the ocean lies 
a low coast plain, the width of which varies from 50 to 250 miles. 

134. The Great Lo^w Plain of North America lies between 
the Atlantic Systems on the east and the Pacific System on the west. 
Tt stretches from the Arctic Ocean to the Gulf of Mexico. 

The Height of Land divides the plain into two gentle slopes, which 
descend toward the Arctic Ocean and the Gulf of Mexico respec- 
tively. A gentle swell extending from north-west to south-east divides 
the northern portion of the plain into two parts. The eastern and 
western basins, so formed, are connected by a break in the water- 
shed, through which the Nelson River empties into Hudson Bay. 
The southern part of the plain is traversed by the Mississippi. 

The tributaries of this river descend the long, gentle slopes of the Atlantic 
and Pacific Systems. 

135. The Relief Forms of a Continent are best understood by 
ideal sections, in which the base line represents the sea-level, and 




Fig. 49. — Section of North America from East to West. 

1, Mt. McKinlcy ; 2, Sierra Nevada ; 3, Rocky Mountains ; 4, Mississippi Valley ; 5, Appa- 
lachian Mountains. 

the scale of heights on the margin represents the elevation of the 
various parts. 

In all such sections the relative vertical dimensions of the land are necessarily 
greatly exaggerated, 

136. Approximate Dimensions of North America. 

Area of continent, 8,400,000 square miles. 

Greatest breadth from east to west, about 3100 miles. 

Greatest length from north to south, about 4500 miles. 

Coast line, 22,800 miles. 

Culminating point, Mount McKinley, 20,464 feet. 



104 



PHYSICAL GEOGRAPHY. 



II. SOUTH AMERICA. 
137. Surface Structure. — The Predominant Mountain-system 
of South America is in the western part of the continent. 

The Secondary Systems 
are in the east. 

The Great Low Plain 
lies between them. 

138. The CordiUera of 
the Andes, which includes 
all the mountains on the 
western border, is the pre- 
dominant system. It is 
composed mainly of two 
approximately parallel 
ranges separated by wide 
and comparatively level 
valleys. On the north 
there are three chains, and on the south 
but one ; in the centre, mainly two. 
The chains are connected by transverse 
ridges, forming numerous mountain- 
knots. 

The Andes form a continuation of the 
Cordillera of the Rocky Mountains. A 
wide depression at the Isthmus of Panama 
marks their separation. 
From this point the Andes 
increase in height toward 
the south, probably reach- 
ing their highest point in 
Chili, where the volcanic 
peak of Aconcagua, 23,910 feet, is believed to be the culminating 
point of South America, and of the Western Continent. 

Nevada de Sorata was formerly believed to be the culminating point of South 
America, but recalculations of the observations have resulted in a loss of nearly 




^^ 



Fig. 50.— Orographic Chart of South America. 

(Light portions, mountains; shaded, plains.) 

1, The Andes Mountains ; 2, Plateau of Quito ; 3, 
Plateau of Bolivia; 4, Aconcagua; 5, Plateau of 
Guiana; 6, Plateau of Brazil; 7, The Orinoco; 8, 
The Amazon ; 9, The Rio de la Plata. 



RELIEF FORMS OF THE CONTINENTS. 



105 




4000 feet of tlie supposed height of Sorata. Some authorities claim that several 
peaks in Bolivia reach an elevation of nearly 25,000 feet. . 

The Andes Mountains terminate abruptly in the precipitous ele- 
vations of Cape Horn. 

Numerous table-lands are included between the parallel ranges: the most 
important are — the plateau of Quito, 9543 feet; the plateau of Pasco, in North 
Peru, 11,000 feet ; the plateau of Bolivia, from 12,000 to 14,000 feet. From most 
of these higher plateaus, volcanic peaks arise. 

139. The Secondary Mountain -systems of South America 
are the plateaus of Brazil and Guiana. They both lie on the eastern 
border. 

The Plateau of Brazil is a table-land whose average height is about 
2500 feet. Narrow 
chains or ridges sepa- 
rate the river-valleys. 

The plateau of Brazil 
forms the watershed be- 
tween the tributaries of 
the Amazon and the La 
Plata. Along the Atlan- 
tic a nearly continuous 
range descends in steep ter- 
races to the ocean. The av- 
erage altitude is more than 
double that of the western 
portion of the plateau. The 
highest peaks are somewhat 
over 8000 feet high. 

The Plateau of Gui- 
ana, smaller than the 
Plateau of Brazil, but about equally elevated, forms the watershed 
between the tributaries of the Orinoco and the Amazon. 

140. The Great Low Plain of South America lies between 
the predominant and the secondary mountain-systems. It is mainly 
of alluvial origin, but slightly elevated, being not more than five 
hundred or six hundred feet in altitude, and is much more level 
than the great plain of Noi'th America. 




Fig. 51.— Gathering Brazilian Dye Wood. 



106 PHYSICAL GEOGRAPHY. 

This plain is drained by the three principal river-systems of the continent, 
by which it is divided into three parts : the Llanos of the Orinoco, the Selvas of 
the Amazon, and the Pampas of the Rio de la Plata. 

The Llanos are grassy plains which, during the rainy season, resemble oui 
prairies, but during the dry weather are deserts. 

The Selvas, or forest plains, are covered by au uninterrupted luxuriant forest. 
The vegetation here is so dense that in some places the broad rivers form the only 
ready means of crossing the country. Near the river-banks are vast stretches of 
swampy ground. 

The Pampas are grassy plains which in some respects resemble the Llanos. 

A coast plain lies between the Andes and the Pacific. It is widest 
near the Andes of Chili, where in some places it is 100 miles in 



26,000 : 

18,000 : 
12,000 : 
6,000 : 

H ' ^<^\ 4 




Fig. 52.— Section of South America from East to West. 

J, Volcano Arequipa ; 2, Lake Titicaca ; 3, Nevada de Sorata ; 4, Central Plain ; 5, Moun- 
tains of Brazil. 

breadth. Between the parallels of 27° and 23° the plain is an abso- 
lute desert, called the desert of Atacama. Here rain never falls 
and vegetation is entirely absent. 

141. Approximate Dimensions of South America. 
Area of continent, about 6,500,000 square miles. 
Greatest breadth from east to west, 32.30 miles. 
Greatest length from north to south, 4800 miles. 
Coast line, 14,500 miles. 

Culminating point, Aconcagua, 23,910 feet. 

142. Contrasts of the Americas. — In both North and South 
America the predominant system lies in the west, the secondary systems 
in the east, and the loiv plains in the centre. 

They differ in the following respects : 

In North America the predominant system is a broad plateau, hav- 
ing high mountain-ranges ; the principal secondary system is narrow 
and is formed of parallel ranges ; the low plains are characterized by 



BELIEF FORMS OF THE CONTINENTS. 101 

undulations, and contain many deep depressions occupied by extensive 

lake-systems. 

In South America the predominant system is narrow; the secondary 
systems are broad ; the low plain is extremely flat, and contains hvi 
few depressions, consequently it has no extensive lake-systems. 

III. EUROPE. 

143. Surface Structure. — The Predominant Mountain-system 
is in the southern part of the continent. 

The Secondary Systems are in the north and east. 
The Great Low Plain lies between the Predominant and Second- 
ary Systems. 

A line drawn from the Sea of Azov to the mouth of the Ehine River, divides 
Europe into tvFO distinct physical regions. The country north of this line is 
sometimes called Low Europe, and that south of it, High Europe. The great low 
plain lies on the north, and the predominant mountain-system on the south. 

144. The Predominant Mountain-system of Europe is com- 
posed of a highly complex series of mountain-systems extending 
along the northern shores of the Mediterranean in a curve, from the 
Straits of Gibraltar to the shores of Asia Minor. The system is 
highest in the centre, where the Alps form the culminating point 
of the system. 

The average elevation of the Alps ranges from 10,000 to 12,000 
feet. The highest peak, Mont Blanc, 15,787 feet, is the culminating 
point of the European Continent. The Matterhorn and Monte Rosa 
are but little inferior in height. On the south-west the system is con- 
tinued to the Atlantic by the Cevennes and adjoining ranges in 
France, and the Pyrenees and Cantabrian in the northern part of 
the Spanish Peninsula. The Pyrenees are an elevated range, with 
peaks over 11,000 feet high. On the east the system extends in 
two curves to the Black Sea by the Carpathian and Transylvanian 
Mountains on the north, and the Dinaric Alps and the Balkan 
Mountains on the south. 

145. Divisions of Predominant System. — The predominant 
mountain-system of Europe may be conveniently regarded as con* 



108 



PHYSICAL GEOGRAPHY. 



sisting of a central body or axis, the Alps, with six projections oi 
limbs — three on the north, and three on the south. 

The three divisions on the north include — 

The Western Division, or the mountains of France, includ- 
ing the mountains lying west of the valleys of the Rhine and the 
Rhone ; 

The Central Division, or the mountains of Germany, situated 




Fig. 53.— Orographic Chart of Europe. (Light portions, mountains; shaded 
portions, plains.) 

1, The Alps ; 2, Mont Blanc ; 3, Pyrenees ; 4 Cantabrian; 5, Sierra Estrella; 6, Sierra 
Nevada; 7, Mountains of Castile; 8, Appennines; 9, Dinaric Alps; 10, Balkan; 11, Pin- 
dus; 12, Taurus ; 13, Caucasus ; 14, Cevennes; 15, Plateau of Auvergne ; 16, Vosges; 17, 
Black Forest; 18, Jura; 19, Hartz; 20, Bohemian Plateau; 21, Carpathians; 22, Hun- 
garian Forest ; 23, Transylvauian Mountains ; 24, Kiolen Mountains ; 25, Urals. 



between the Western Division and the upper valleys of the Oder 
and the Danube; 



RELIEF FORMS OF THE CONTINENTS. 



109 



The Eastern Division, or the mountains of Austria-Hungary, situ- 
ated between the Central Division and the Black Sea. 

These divisions contain a liighly complicated system of minor elevations. 
Their complexity is due to the frequent intersection of the north-eastern and 
north-western trends. Basin-shaped plateaus, like the Bohemian and Transyl- 
vanian, are thus formed. 

The Western Division includes most of the mountains of France, as the 
Cevennes, the mountains of Auvergne, and the Vosges Mountains. 

The Central Division includes the Jura Mountains in Switzerland, the Swiss 
and the Bavarian Plateaus, the Black Forest Mountains, the Hartz Mountains, 
and the Bohemian Plateau. 

The Eastern Division includes most of the mountains of Austria, as the 
Carpathians, the Hungarian Forest, and the Transylvanian Mountains. 

146. The Secondary Mountain-systems of Europe comprise 
the system of the Scandinavian Peninsula, the Ural Mountains, and 
the Caucasus Mountains. 

The System of the Scandinavian Peninsula includes the elevations 
of Norway and Swe- 
den. With the excep- _^ 
tion of the Kiolen ^^ 
Mountains in the north, 
the system does not 
embrace distinct moun- 
tain-ridges, but consists 
mainly of a series of 
broad plateaus that de- 
scend abruptly on the 
west in numerous deep- 
ly-cut fiord valleys that 
were formed by gla- 
ciers or slowly moving 
masses of ice, and which 
were subsequently par- 
tially submerged. Through these fiord valleys the sea penetrates 
nearly to the heart of the plateau. The more gradual eastern 
slopes are occupied by numerous small lakes. 

The System of the Urals is composed of a moderately elevated 




Fig. 54 —Fiord on Norway Coast. 



no PHYSICAL QEOGBAPHY. 

range extending from the Arctic Ocean on the north to the plains 
of the Caspian on the south. The elevated island of Nova Zem- 
bla may be considered as forming a part of its northern prolon- 
gation. 

The Caucasus Mountains extend from Europe into Asia. They 
contain peaks exceeding in elevation those of the Alps. The high- 
est of these peaks are found in Asia. 

147. The Great Lo-w Plain of Europe lies between the pre- 
dominant and secondary mouutain-systems, and stretches north- 
eastward from the Atlantic to the Arctic. It is remarkably level, 
and is highest in the middle, where the Valdai Hills form the prin- 
cipal watershed of Europe. Westward the plain is continued under 
the North Sea to the British Isles, where a few inconsiderable ele- 
vations occur. 

South of the Alps the large plain of the Po River stretches across 
the northern part of Italy. 

Europe projects on the south in three mountainous peninsulas; 
The Iberian Peninsula, including Spain and Portugal ; 

The Italian Peninsula ; 

The Tur CO- Grecian Peninsula. 

The Iberian Peninsula. — The principal mountains are the Sierra Estrella, 
the mountains of Castile, and the Sierra Nevada. The Pyrenees separate the 
Peninsula from France. The Cantabrian Mountains extend along the northern 
coast. 

The Italian Peninsula contains the Apennines, extending mainly in the 
direction of the north-western trend. 

The Turco-Grecian Peninsula.— The Dinaric Alps extend along the coast 
of the Adriatic; the Balkan Mountains extend from east to west, through 
Turkey; and the Pindus from north to south, through Turkey and Greece. 

148. Approximate Dimensions of Europe. 
Area of continent, 3,700,000 square miles. 
Coast line, 19,500 miles. 

Greatest breadth from north to south, 2400 miles. 
Greatest length from north-east to south-west, 3370 miles. 
Culminating point, Mont Blanc, 15,787 feet. 



RELIEF FORMS OF THE CONTINENTS. 



Ill 



IV. ASIA. 
149. Surface Structure. — The Predominant Mountain-system 
is in the south. 
The Secondary Systems surround the Predominant 'System. 




Fig. 55. — OrograpMc Chart of Asia. (Light portions, mountains; shaded per. 

tions, plains.) 

1, Himalaya Mountains ; 2, Karakorum ; 3, Kuen-lun ; 4, Belor ; 5, Thian Shan ; 6, 
Altai ; 7, Great Kinghan ; 8, Yablonoi ; 9, Nanling ; 10, Peling ; 11, Vindhya ; 12, Ghauts ; 
13, Hindoo-Koosh ; 14, Elburz ; 15, Suliman ; 16, Zagros ; 17, Taurus ; 18, Caucasus ; 19, 
Asiatic Island Chain. 

The Great Low Plain lies on the north and west, between the 
mountain-systems of Asia and the secondary system of the Urals. 

Europe and Asia are sometinaes considered as geographically united in one 
grand division, called Eurasia. 

150. The mountain-systems of Asia are nearly all connected in 
one huge mass, which extends in the line of the north-east trend, 
from the Arctic to the Indian Ocean. Though in reality one vast 



112 



PHYSICAL GEOGRAPHY. 



system, yet they are most conveniently arranged in one predominant 

and several secondary systems. 

The Predominant System is the plateau of Thibet, the loftiest 
table-land in the world. It is between 15,000 and 16,000 feet high, 
and is crossed by three huge, nearly parallel mountain-ranges : the 
Himalayas on the south, the Kuen-lun on the north, and between 
them the Karakorum. 



-V» -_ 




"-a 




£•:•>*■ . 


■* 




- -- ■?* ^-- 


i^^Ssw**-^^^ 


mSSHkl. ^f^iHlHP^^HBau^ . 







Fig. 56.— Zemu Glacier and Mount Siniolchum in the Himalayas. 



151. The Secondary Systems lie on all sides of the predomi- 
nant system, though mainly on the north and east of the predomi- 
nant system. The Asiatic Continent projects on the south in the 
three mountainous peninsulas of Arabia, Hindostan, and Indo- 
China. 

On, the north and east of the plateau of Thibet is an extended 
region called the plateau of Gobi, considerably lower than the sur- 
rounding country. The Kiien-lun and Great Kinghan Mountains 
bound it on the south and east, and the Altai Mountains on the north. 



BELIEF FORMS OF THE CONTINENTS. 113 

On the west lie the Thian Shan and Altai, which by their open val- 
leys afford ready communication with the low plains on the west. 

The plateau of Gobi varies in height from 2000 to 4000 feet. The greatest 
depression is in the west, and is occupied by Lake Lop and the Tarim River. 
A small part of the region near the mountain-slopes is moderately fertile ; the 
remainder is mainly desert. 

The Altai Mountains are but little known, but some of their peaks exceed 
12,000 feet. They are continued eastward by the Yablonoi Mountains. East of 
the plateau of Gobi a range extends north-easterly through Mantchuria. 

On the south and west of Thibet lie the plateaus of Iran, Armenia, 
and Asia Minor. 

The Plateau of Iran includes Persia, Afghanistan, and Beloochis- 
tan. It is a basin-shaped region from 3000 to 5000 feet high. The 
Elburz and Hindoo-Koosh Mountains form its borders on the north, 
the Suliman, on the east, and the Zagros, on the south and west. 

The Suliman Mountains rise abruptly from the plains of the Indus. Across 
these mountains occurs the only practicable inland route between Western Asia 
and the Indies. 

The Plateaus of Armenia and Asia Minor lie west of the Plateau 
of Iran. Armenia is 8000 feet high, and bears elevated mountains: 
Mount Ararat, 16,900 feet, is an example. On the west, the penin- 
sula of Asia Minor, or Anatolia, extends between the Black and 
Mediterranean Seas, and is traversed by the Taurus Mountains. 

The Caucasus Mountains lie north of the plateau of Armenia. 
They are an elevated range extending between the Black and Cas- 
pian Seas, and forming part of the boundary-line between Europe 
and Asia. Mount Elburz, the "Watch-Tower," the culminating 
peak, is 18,493 feet high. 

The Arabian Plateau occupies the entire peninsula of Arabia. 
It is separated from the plateau of Iran by the Persian Gulf and 
the valleys of the Tigris and the Euphrates. 

The Plateau of Decean occupies the lower part of the peninsula 
of Hindostan. It is crossed on the north by the Vindhya Moun- 
tains, and along the coasts by the Eastern and Western Ghauts. 

The Peninsula of Indo- China is traversed by a number of moun- 
tain-ranges which diverge from the eastern extremity of the Hima- 



114 PHYSICAL GEOQBAPHY. 

lay as. The Nanling and the Peling mountains extend from east to 
west through China. 

152. The Great Low Plain is a continuation of the European 
plain. It extends from the Arctic Ocean south-westerly to the 
Caspian and Black Seas. It is hilly on the east, but level on 
the west. South of the 60th parallel it is comparatively fertile- 
Near the shores of the Arctic are the gloomy and inhospitable 
Tundras. 

The Tundras are vast regions which in summer are covered with occasional 
moss-beds, huge shallow lakes, and almost innumerable swamps, and in winter 
with thick ice. The tundras are caused as follows : The rivers that flow over 
the immense plain of Asia rise in the warmer regions on the south. The thawing 
of their upper courses while their lower courses are still ice-bound, permits large 
quantities of drift ice to accumulate at their mouths, which, damming up the 
water, causes it to overflow the adjoining country. 

Depressions of the Caspian and the Sea of Aral.- — Two re- 
markable depressions occur in the basius of the Caspian and the Sea 
of Aral, and that of the Dead Sea. These are all considerably below 
the level of the ocean. The waters of the Caspian and the Sea 
of Aral were probably once connected in a great inland sea. 

The Smaller Asiatic Plains are drained by several river-systems 
These are the Plain of Mantchuria, drained by the Amoor; the 
Plain of China, drained by the Hoang-Ho and the Yang-tse-Kiang; 

5rA4 7« 







16 



Fig. 57.— Section of Asia from North to South. 
1, Cape Comorin ; 2, Deccan ; 3, Plain of India ; 4, Himalayas ; 5, Everest ; 6, Kaen- 
lun ; 7, Karakorum; 8, Thibet ; 9, Upper Tartary; 10, Ararat; 11, Elburz; 12, Thian 
Shan ; 13, Altai ; 14, Mountains of Kamtchatka ; 15, Arctic Ocean, Mouth of Yenesei. 

the Plain of India, drained by the Indus, the Ganges, the Brahma- 
pootra, and the Irrawaddy ; and the Plain of Persia, drained by the 
Tigris and the Euphrates. 

153. Approximate Dimensions of Asia. 

Area of continent, 17,500,000 square miles. 

Coast line, 35,000 miles. 

Greatest length from north-east to south-west, 7500 miles. 



RELIEF FORMS OF THE CONTINENTS. 



115 



Greatest breadth from north to south, 5166 miles. 
Culminating point, Mount Everest, 29,000 feet. 

154. Comparison of the Relief Forms of Europe and Asia. 
— In both Europe and Asia the chief elevations are in the south and 
the great low plains in the north. Asia, like Europe, extends 
toward the south in three great peninsulas : Arabia, Hindostan, and 
Indo-China. 

V. AFRICA. 

155. Surface Structure. — Nearly the entire continent of Africa 
is a moderately elevated plateau. It, therefore, has no great low 
plains ; but the interior 

is lower than the mar- 
ginal mountain-systems, 



and, in this respect, the 
true continental type, 
high borders and a low 
interior, is preserved. 

156. The Predomi- 
nant Mountain-system is 
in the east. 

The Secondary Sys- 
tems are in the south, 
west, and north. 

The great interior de- 
pression is in the middle, 
and is surrounded by the 
predominant and second- 
ary systems. 

A narrow, low plain 
extends along most of the 
coast of Africa. This 
plain is broadest on the 
north-west, between the 
plateau of the Sahara and the Atlas Mountain-system. 

157. The Predominant Mountain-system extends along the 




Fig. 58.— Orographic Chart of Africa. 

(Light portions represent mountains ; shaded por- 
tions, plains.) 

1, Abyssinian Plateau ; 2, 3, Kenia and Kilimand- 
jaro; 4, Lupata; 5, Dragon; 6, Nieuveldt ; 7, Mo- 
cambe ; 8, Crystal ; 9, Cameroons ; 10, Kong ; 11, Atlas ; 
12, Lake Tchad ; 13, Madagascar. 



116 PHYSICAL GEOGRAPHY. 

entire eastern shore, from the Mediterranean Sea to the southern' 
extremity of the continent. It is highest near the centre, in the 
plateaus of Abyssinia and Kaffa. The culminating point is, probably, 
to be found in the volcanic peaks of Kenia and Kilimandjaro, 
whose estimated heights are about 19,000 feet. In the Abyssinian 
plateau, on the north, the average elevation is from 6000 to 8000 
feet. From the plateau, in detached groups, arise peaks, the highest 
of which are over 15,000 feet. 

From the Abyssinian plateau the system is continued northward to 
the Mediterranean by a succession of mountains which stretch along 
the western shores of the Red Sea. Some of the peaks are from 6000 
to 9000 feet high. South of the plateau of Kaffa the system is con- 
tinued by the Lupata and Dragon Mountains to the southern extrem- 
ity of the continent. The Zambesi and Limpopo Rivers discharge 
their waters into the Indian Ocean through deep breaks in the system. 

158. Secondary Systems. — On the south the Nieuveldt and 
Snow Mountains stretch from east to west, with peaks of over 10,000 
feet. Table Mountain is on the south. 

On the west the Mocambe and Crystal Mountains extend from the 
extreme south to the Gulf of Guinea. Near the northern end of 
this range, but separate from it, are the volcanic peaks of the Came- 
roons Mountains, 13,000 feet high. 

The Kong Mountains extend along the northern shores of the 
Gulf of Guinea in a general east-and-west direction. Some of the 
peaks are snow-capped. In the extreme north of Africa are the 
Atlas Mountains, which rise from the summit of a moderately ele- 
vated plateau. Some of the peaks are 13,000 feet high. 

159. The Great Interior Depression north of the equator is di- 
vided into two distinct regions. A straight line extending from Cape 
Guardafui to the northern shores of the Gulf of Guinea marks the 
boundary. The mountain-systems north of this line have a general 
east-and-west direction ; those south of it a north-and-south direction. 

The Plateau of the Sahara occupies the northern part of the inte- 
rior depression. Its general elevation is about 1500 feet, though 
here and there plateaus of from 4000 to 5000 feet occur, and even 



RELIEF FORMS OF THE CONTINENTS. 



117 



short 5nountain-ranges with peaks of 6000 feet. The main portion 
of the region is covered with vast sand-fields, with occasional rocky 
masses, and is, for the greater part, an almost absolute desert. 

Near Long. 14° E. from Greenwich, in the district of Fezzan, the plateau is 
divided from north to south 
by a broad valley, in which 
occur many remarkable de- 
pressions, some of which 
are several hundred feet 
below the level of the 
Mediterranean. Here fer- 
tile spots, called oases, are 
common. 

South of the Sahara 
is the Soudan, a re- 
markably well-watered 
and fertile region. 
Lake Tchad occupies 
the greatest depression. 
The interior, which 
lies south of this, is 
but little known. It is, probably, a moderately elevated plateau 
Extensive lake basins — Albert Nyanza, Victoria Nyanza, and Tan- 
ganyika — lie near the predominant mountain-system. 

160. Approximate Dimensions of Africa. 

Area of continent, 12,000,000 square miles. 

Coast line, 16,000 miles. 

Greatest breadth from east to west, 4800 miles. 

Greatest length from north to south, 5000 miles. 

Culminating point, Mount Kenia, or Kilimandjaro, about 19,000 feet. 




Fig. 59.— Scene at Biskra, in the Sahara. 



VI. AUSTRALIA. 

161. Surface Structure. — The Predominant Mountain-system 
is in the east. 

The Secondary Systems are in the west and north-west. 

The Great Low Plain lic3 between the predominant and second* 
ary systems, and slopes gently to the southern coast. 



118 



PHYSICAL GEOGRAPHY. 



The Predominant System extends along the entire eastern shore, 
from Torres Straits to the southern extremity of Tasmania. It is, 
for the most part, composed of broad plateaus. The system is highest 

in the south-east, where the 
name Australian Alps is given 
to the range. Moiint Kosciusko, 
7000 feet, probably forms the 
culminating point of the Aus- 
tralian Continent. 

The system descends abruptly 
on the east, and by gentle slopes 
on the west to the low plains 
of the interior. 

162. The Secondary Sys- 
tems, on the west and north- 
west, are of but moderate ele- 
vation. 




Fig. 60.— Orographic Chart of Australia. 

'White portions, mountains ; shaded 
portions, plains.) 



1, Australian Alps; 2, Kosciusko; 3, 4, 5, 
Secondary Systems ; 6, Murray River. 



163. The Great Low Plain lies 
in the interior. Accurate informa- 
tion as to its peculiarities is yet 
wanting. A moderate elevation on 
the north connects the eastern and western systems. The south-eastern portion, 
which is the best known, is well watered and remarkably fertile. Basin-shaped 
valleys are found in the west. The lower parts are occupied by lakes Eyre, 
Torrens, and Gairdner. 

164. Approximate Dimensions of Australia. 
Area of continent, 3,000,000 square miles. 

Coast line, 10,000 miles. 

Greatest length from east to west, 2400 miles. 
Greatest breadth from north to south, 2000 miles. 
Culminating point, Mount Kosciusko, 7000 feet. 

165. Contrasts of Africa and Australia. — In the north, the 
African Continent resembles Europe and Asia in the arrangement of 
its forms oi relief. In the south, it resembles the Americas. As a 
whole, the African Continent resembles Australia more closely than 
any other. In both Africa and Australia the predominant system 
is in the east, and extends along the entire coast. In each the seo- 



RELIEF FORMS OF THE CONTINENTS. 



119 



ondary systems are in the west and north. But Africa terminates in 
a plateau which descends abruptly to the sea, while Australia is ter- 




Fig. 61.— Australian Scenery. 



minated by a great loiv plain which descends by long, gentle slopes from 
the interior. 



-.oj^lc 



SYLLABUS. 

Eocks consist of various mixtures of substances called minerals. Rock -masses 
are divided, according to their origin, into igneous, aqueous, and metamorphic, to 
which are sometimes added kalian. According to their condition, rocks are 
divided into stratified and unstratified ; according to the presence or absence of 
arganic remains, into fossiliferous and non-fossiUferous. Unstratified rocks are 
sometimes called crystalline. Aqueous rocks are sometimes called sedimentary. 

Aqueous rocks are stratified. Igneous rocks are unstratified. Metamorphic 
Tocks were originally stratified, but lost their stratification through metamor- 
phjsm. (^olian rocks are roughly stratified. 



120 PHYSICAL GEOOBAPHY^ .:.:,]. 

The earth's oldest or primitive rocks were either formed hy the first cooling 
of the outside of the melted earth, or were thrown down as sediment in the 
primitive ocean. It is doubtful whether these rocks have ever been reached. 

Aqueous rocks may contain fossils. Igneous rocks never contain fossils. 
Metamorphic rocks, in rare instances, may contain fragments of fossils. 

Geological time is divided into eras ; the eras are subdivided into periods ; the 
periods into epochs ; and the epochs into ages. 

There are six geological eras ; viz., the Azoic, the Eozoic, the Palseozoic, the 
Mesozoic, the Cenozoic, and the Era of Man. 

The Azoic Era includes the Astral Period and the Archaean Period. 

The Eozoic Era includes the Algonkian Period. 

The Palaeozoic Era includes the Silurian Period, or the Period of Invertebrates, 
the Devonian Period, or the Period of Fishes, and the Carboniferous Period, or 
the Period of Coal Plants. 

The most important agencies now producing change in the earth's crust are 
the Heated Interior, Erosion or Denudation, including Weathering, Corrasion, 
and Transportation ; Wind Corrasion and Transportation ; Avalanches and Land- 
slides; Ocean Waves, and Man. 

There is more water than land surface on the earth, in proportion of 25 : 9, or 
as 5'' : 3^ 

The land-masses surround the north pole in the shape of an irregular ring. 

Nearly all the land-areas are collected in one hemisphere, and the water-areas 
in another hemisphere. 

The northern continents are almost entirely in the temperate latitudes ; the 
southern continents are mainly in the tropics. 

The land-masses may be divided into three doublets, consisting of pairs of 
northern and southern continents, almost or entirely separated from each other. 

There are two great systems of trends or lines of direction. These trends are 
north-east and north-west. 

The northern continents are characterized by deeply indented coast lines ; the 
southern are comparatively simple and unbroken. Europe is the most, and Africa 
the least, deeply indented of the continents. 

One-seventeenth of the land-area is composed of islands. 

Islands are either continental or oceanic. 

The smaller continental islands include fiord islands, delta islands, low mud- 
flats and sand-bar islands, and small, high, rocky islands. 

There are four successive stages in the formation of a coral island or atoll : 
1. The fringing reef ; 2. The barrier reef; 3. The encircling reef; 4. The coral 
island or atoll. 

The greatest elevations and depressions in the earth's surface are small when 
compared with its size. 

Low lands are either plains or hills. High lands are either plateaus or moun- 
tains. 

Alluvial plains are lacustrine, fluviatile, or marine. Plains are divided, ac- 



SYLLABUS. 121 

cording to their position, into coastal, inland, and worn-down mountain low lands, 
old plains or peneplains. They are divided, according to the materials that form 
them, into river-made plains, dust plains, and lava plains. 

Plateaus, according to their position, are marginal or interment ; according to 
their age, they are young or old. 

Mountains may be divided into three classes : 1. Mountains by flexure ; 2. 
Mountains by fracture ; 3. Mountains by injection of lava between strata. 

Valleys are either longitudinal or transverse. 

All continents have high borders and a low interior. The highest border faces 
the deepest ocean. 

North and South America resemble each other in the arrangement of their 
relief forms. Their predominant systems are in the west ; their secondary sys- 
tems are in the east ; their great low plains are between the predominant and 
secondary systems. 

The predominant system of North America is the Cordillera of the Eocky 
Mountains. The secondary systems are — the Appalachian system, the plateau 
of Labrador, the Height of Land, and the Arctic plateau. 

The predominant system of South America is the Cordillera of the Andes. 
The secondary systems are — the plateaus of Guiana and Brazil. The great low 
plains are — the Llanos of the Orinoco, the Selvas of the Amazon, and the Pampas 
of the La Plata. 

Europe and Asia resemble each other. Their predominant systems are in the 
south ; their great low plains are north of their predominant systems. The pre- 
dominant system of Europe is the Alps. 

The secondary systems of Europe are— the mountains of the Scandinavian 
Peninsula, the Ural Mountains, and the Caucasus Mountains. 

The predominant mountain-system of Asia is the plateau of Thibet. 

The secondary systems of Asia are— the plateau of Gobi, the Thian-Shan and 
Altai Mountains, the plateau of Indo-China, the plateau of Deccan, the plateau 
of Iran, the plateau of Asia Minor, and the plateau of Arabia. 

The predominant mountain-system of Africa includes the mountains of the 
eastern coast. - 

The secondary systems include the Nieuveldt and Snow Mountains in the 
south, the Mocambe, Crystal, Cameroons, and Kong Mountains in the west, and 
the Atlas Mountains in the north. 

The predominant mountain-system of Australia includes the mountains of the 
eastern coast. 

The secondary system includes the mountains found in the west and north. 

Africa and Australia resemble each other. Their predominant systems ara in 
the east; their secondary systems are in the west and north; their depressed 
areas are between the two. 



122 PHYSICAL GEOGRAPHY. 



, REVIEW QUESTIONS. 

What two elementary substances form the greater part by weight of the 
earth's crust? 

Into what classes may rocks be divided according to their origin? According 
to their condition? According to the presence or absence of fossils? 

What is paleontology ? 

Into what two classes may igneous rocks be divided ? Define ^olian rocks ; 
fragmental rocks ; sedimentary rocks ; crystalline rocks. What do you under- 
stand by the term primitive rocks ? 

Define Azoic Era, Eozoic Era, Palaeozoic Era, Mesozoio Era, and Cenozoic Era. 

Explain the nature of the changes in the earth's surface caused by the 
atmosphere ;" by water ; by the agency of man. 

Describe in full the process of weathering. Define erosion, denudation, corra- 
sion, wind erosion, transportation. 

What is meant by the load of a river? How are dunes formed ? 

What must be the sides of two squares whose areas represent the relative land- 
and water-areas of the earth? What are the actual areas in square miles? 

How would you draw a circle around the earth which will divide it into land 
and water hemispheres ? 

What do you understand by lines of trend? Define lagoons; dunes. 

Describe the American island chains ; the Asiatic chains. 

Describe the Australasian island chain ; the Polynesian chain. 

Which are the higher, volcanic islands or coral islands ? Why ? 

Name the principal steps or stages in the progress of formation of a cora. 
island. State Darwin's hypothesis for the formation of coral islands. State any 
other hypotheses that have been proposed for coral formation. 

To what do plains owe their level surface ? 

Distinguish between lacustrine, fluviatile, and marine plains. What single 
term will include all these plains? 

Distinguish between coastal and inland plains. Describe the formation of 
peneplains. 

Distinguish between marginal and intermont plateaus. 

Define mountain-system ; axis of mountain-system. What is Orology ? 

Explain the manner in which mountains are formed. 

Into what classes may mountains be divided according to their origin ? 

Define block mountains. What is meant by a dissected block mountain? 
Embayed mountain? 

Distinguish between a longitudinal and a transverse valley. 

Give a short account of the surface structure, or the arrangement of the high 
and low lands, of North America. Of South America. Of Europe. Of Asia. 
Of Africa. Of Australia. Which of these resemble each other ? In what respect 
do they all resemble one another? 



SYLLABUS. 123 

Name the culminating points of each of the continents. Name the predomi- 
nant and secondary mountain-systems of each of the continents. 

How many times larger is Asia than Australia? Than Europe? Africa? 
North America ? South America ? 

North America. 
Describe the Cordillera of the Eocky Mountains. 
Where is the Great Basin ? By what mountains is it surrounded ? 
Name the principal mountains of the Appalachian system. 
What rivers drain the great low plain of North America ? 

South America. 
Describe the Cordillera of the Andes. 
Name the principal plateaus of the Andes. 
Where is the plateau of Guiana ? Of Brazil ? 
What three large river-systems drain the great low plain of South America ? 

Europe. 

Describe the predominant mountain-system of Europe. 

Describe the chain of the Alps. 

What river-systems divide its northern slope into three divisions? Name the 
principal mountains of each division. 

What three peninsulas project southward from the southern slopes of the pre- 
dominant mountain-system ? Name the principal mountains of each peninsula. 

Asia. 

Describe the predominant mountain-system of Asia. 

What mountains form the northern boundary of the plateau of Gobi ? The 
southern boundary ? 

What mountains form the boundaries of the plateau of Iran ? Is Arabia a 
plateau or a plain? 

Describe the great low plain of Asia. 

Africa. 
Describe the predominant mountain-system of Africa. 

Where are the Mocambe Mountains ? The Crystal Mountains, the Cameroons, 
the Atlas, the Kong, the Lupata, and the Dragon ? 

Australia. 
Describe the predominant mountain-system of Australia. 
Describe the secondary mountain-system. The great low plain. 



PART III. 
THE WATER. 



Source and Disposal. — By contact of air with the water areas 
invisible vapor continually passes into the atmosphere. When suf- 
ficiently cooled, this vapor again becomes visible, and descends as 
fog, cloud, mist, dew, rain, hail, sleet, or snow. The average annual 
rainfall of the United States is about thirty inches. This means 
that a total of about 1500 cubic miles of water falls in the forms 
given above in this country each year. It is thought that about 
half of this water evaporates (page 221), that about one-third of it 
runs off over the surface, and that the remaining one-sixth is taken 
up by plants or sinks into the earth as ground loater. This ground 
water may be thought of as forming a sea many miles in depth and 
extending through the rock sphere beneath the land surface from 
ocean to ocean. Thus the water sphere is really continuous around 
the globe. The upper surface of the ground sea, called the water 
table, is not level but is roughly parallel with the surface of the 
land. In lakes, marshes, and streams the water table stands at 
the surface of the ground. 

This section is designed to show the depth at which this ground 
water lies, its destructive action in the erosion and corrosion it 
produces when it seeks lower levels in the form of rivers, falls, and 
lakes ; how its solvent action is increased by carbon dioxide in 
solution ; and finally its effects on salt and limestone, on caverns 
and sink or shallow holes. Its constructive action is to be seen in 
deposits such as veins, stalactites, and stalagmites. The ground 
water makes its reappearance in the form of springs, wells, artesian 
wells, mineral springs, hot springs, and geysers. 

124 



PHYSICAL PROPERTIES OF WATER. 125 

SECTION I. 
CONTINENTAL WATERS. 

»oj«<oo 



CHAPTER I. 

Physical Properties of ^A/'ater. 

166. Composition. — Water is formed by the chemical combina- 
tion of oxygen and hydrogen, in the proportion, by weight, of eight 
parts of oxygen to one part of hydrogen ; or, by volume, of one 
part of oxygen to two parts of hydrogen. 

167. Properties. — Pure water is a colorless, transparent, taste- 
less, and inodorous liquid. It freezes at 32° Fahr., and, under the 
ordinary pressure of the atmosphere, boils at 212° Fahr. 

Water exists in three states : solid, liquid, and gaseous. Under ordinary cir- 
cumstances it freezes at 32°. It evaporates, or passes off from the surface as 
vapor, at all temperatures, even at 32° ; but it is only at the boiling-point that 
the vapor escapes from below the surface as well as at the surface of the liquid. 

Heated in open vessels, under the ordinary pressure of the atmosphere, the 
temperature of boiling water cannot be raised higher than 212°, any increase of heat 
only causing it to boil more rapidly. Heated in closed vessels, which prevent 
the escape of steam, and permit the pressure to accumulate, its temperature can 
be raised very high. Conversely, on high mountains, where the pressure of the 
atmosphere is lower than at the level of the sea, water boils at temperatures 
lower than 212° Fahr. 

168. Maximum Density of Water. — A pint of cold water is 
heavier than a pint of warm water, because, as water is cooled, it 
contracts and grows denser. The coldest pint of water, however, is 
not the heaviest. The heaviest pint of water is water at the tem- 
perature of 39.2° Fahr. This temperature, therefore, is called the 
temperature of the maximum density of water. If water at this 
temperature be heated, it becomes lighter, or expands ; if water at 



126 PHYSICAL GEOGRAPHY. 

this temperature be cooled, it also becomes lighter or expands until 
ice is formed, which floats on the water. When at the temperature 
of its maximum density, water is 7.2° warmer than the freezing- 
point. 

1G9. Effect of the Maximum Density of Water on its 
Freezing. — If cooling water continued to contract until freezing 
began, the ice first formed would sink to the bottom, and, this 
continuing, the entire mass would soon become solid. In this 
manner great bodies of fresh water, in times of cold, might freeze 
throughout, when not even the heat of a tropical sun could entirely 
melt them. 

But for this curious physical property of water, at least three-fourths of the 
globe would be incapable of sustaining its present life. 

The entire floor of the ocean, both in the tropics, and in the temperate and 
the polar regions, is covered with a layer of cold, salt water, at nearly the tem- 
perature of its maximum density. In the tropics the surface-water is warmer 
and lighter than this dense layer, and in the polar regions it is colder and 
lighter. 

Ground or Atichor Ice. — In very cold climates, ice, called ground or anchor ice, 
sometimes forms around sharp-pointed rocks on the bottom of rivers. When the 
ice deposit is of sufiBcient size its buoyancy brings it to the surface, along with 
the entangled rocks. The ice floating with the river current thus transports 
the rock or other mineral matter often for considerable distances. 

170. Specific Heat of "Water. — Another remarkable physical 
property of water — its specific heat — enables it to play an important 
part in the economy of the earth. 

The specific heat of a body is the quantity of heat-energy required 
to produce a definite increase of temperature in a given weight of 
that body. Water has a very high specific heat ; that is, a given 
quantity of water requires more heat-energy to warm it, and gives out 
more heat-energy on cooling, than, an equal quantity of any other 
common substance. 

The quantity of heat required to raise a pound of ice-cold water to 212°, 
would heat a pound of ice-cold iron to a bright-red heat, or to about 1600° Fahr. ; 
or, conversely, a pound of boiling water, cooling to the freezing-point, would give 
out as much heat as a pound of red-hot iron cooling to 32° Fahr. 



PHYSICAL PROPERTIES OF WATER. 127 

The enormous capacity of water for heat is of great value to the 
life of the earth. The oceanic waters are vast reservoirs of heat, 
storing heat in summer and giving it out in winter. The great 
specific heat of water prevents it from either heating or cooling 
rapidly. Large bodies of water, therefore, in any region, prevent 
great extremes of heat and cold. 

171. Heat Absorbed or Emitted during Change of State. 
■ — During the conversion of a solid into a liquid, or a liquid into 
a vapor, a large quantity of heat-energy is absorbed. This heat- 
energy does not increase the temperature of the body, and, therefore, 
cannot be detected by the thermometer. The heat-energy is then 
in the condition of stored or potential energy, sometimes called latent 
heat. When water-vapor condenses into a liquid, or when liquid 
water freezes, the stored heat-energy again becomes sensible as heat. 

In freezing, water gives out heat, and raises the mean temperature 
of the surrounding air. 

In melting, ice takes in heat, and loivers the mean temjoerature of the 
surrounding air. 

172. Stored Heat-energy of Ice-cold Water. — Water has a 
higher latent heat than any other common substance. In order 
to heat a pound of water 1° Fahr. an amount of heat called a heat- 
unit, or a pound-degree, is required. Before one pound of ice at 
32° Fahr. can melt and form one pound of water at 32° Fahr., it 
must take in H^ heat-units ; and yet a thermometer, plunged in the 
water from melting ice, will indicate the same temperature as when 
entirely surrounded by lumps of the unmelted material. 

The great latent heat of ice-cold water has an important influence on the freez- 
ing of large bodies of water, since, after the surface-layers have reached the tem- 
perature of the freezing-point, they have still 142 heat-units to lose before they can 
solidify. Again, when ice reaches a temperature of 32° Fahr., it has still 142 
heat-units to absorb before it can melt. Were it not for this fact, destructive 
floods would often result from the rapid melting of the winter's accumulation 
of snow and ice. 

173. Stored Heat-energy ofWater-vapor. — Before one pound 
of water can pass off as vapor, it must take in sufficient heat to raise 



128 PHYSICAL GEOGRAPHY. 

nearly 1000 pounds of water 1° Fahr. The vapor which then 
escapes is still at the same temperature as the water from which 
it came. I%e 1000 heat-units, or pound-degrees of heat, have been 
rendered latent, and have no influence on the thermometer. 

When the vapor in the air is condensed as rain, snow, hail, dew, 
fog, cloud, or mist, the stored heat-energy again becomes sensible. 
Much of the vapor which is formed in the equatorial regions is car- 
ried by the winds to high latitudes, where, on condensing, it gives 
out its heat and moderates the intense cold which would otherwise 
exist. 

174. Solvent Po'wers. — Water is one of the best solvents of all 
common substances. During the constant washings of the continents 
by the rains, the surfaces are cleansed from decaying animal and 
vegetable matters, which are partly dissolved and are thus carried in 
solution by the rivers into the ocean. The atmospheric waters in a 
similar way cleanse the air of many of its impurities. 

175. "Water is the Main Pood of Animals and Plants. — By 
far the greater part of the bodies of animals and plants is composed 
of water. Without large quantities of water no vigorous life can 
be sustained in any locality. 

Deserts are caused by the absence of water. 



«>>»Jc 



CHAPTER II. 

Drainage. 

176. Drainage. — The water which falls from the atmosphere as 
rain, hail, or snow, either sinks through the porous strata and is 
drained under ground, or runs directly off the surface. Thus result 
two kinds of drainage — Subterranean and Surface. 

The rapidity of drainage is greater in open, porous strata, such as 
are formed of rock waste, than in hard rocks, such as granites. The 
freezing of the soil may cause all the drainage to take place at the 



DRAINAGE. 



129 



surface. Where the surface soil is underlaid by readily soluble for- 
mations, such as limestone, crevices in the rocks are enlarged by 
solution, and the surface-waters may sink so rapidly into the 
ground as either to decrease greatly the volume of the surface 
streams, or to obliterate them entirely. 

177. Subterranean Drainage. — The water which sinks through 
the porous strata continues descending until it meets impervious 
layers, when it either runs along their surface, bursting out as springs 
at some lower level, where the layers outcrop, or it collects in sub- 
terranean reservoirs. The origin of all springs is to be traced to 
subterranean drainage. 

Underground streams sometimes attain considerable size. In portions of the 
Swiss Jura, streams burst from the sides of hills in suificient volume to turn the 
wheels of moderately large mills. In a few instances, the subterranean streams 
can be navigated for considerable distances, as in the Mammoth Cave of Ken- 
tucky, or in the Grotto of Adelsberg, near Trieste. 

178. Surface Drainage. — The water that is drained directly 
from the surface, either runs down the slopes in rivulets and rills, 
which, uniting with larger streams, 
is poured directly into the ocean, 
or it collects in the depressions 
of basin-shaped valleys, where, 
having no connection with the 
ocean, it can be discharged by 
evaporation only. Thus arise 
two kinds of surface drainage — 
oceanic and inland. 

179. Wells, — The water that has sunk into the slopes of hills 
slowly descends to the lower land of the valleys, where it either 
escapes in springs, or collects in the strata near the surface. In 
nearly all parts of the valley, water may be obtained by sinking 
wells at depths varying from 10 to 30 feet. 

180. Springs are the outpourings of the subterranean waters, 
They may occur as — 

(1) Hill-side Springs. — On hill-sides, where a bed of sand, gravel, 
9 




Fig. 62.— Hill- side Spring. 



130 



PHYSICAL GEOGRAPHY. 




or other porous material, rests on an impervious bed of clay or hard 

rock. Thus in the hill- 

^li ---^i ' l^Vft^i side shown in Fig. 62, 

the upper portion of 
the hill is formed of a 
bed of sand, 8, resting 
on a bed of clay, C, 
or other impervious 
layer. Rain falling on 
the surface sinks down 
through the porous 
sand until it reaches 
the impervious layer, 
and either runs down 
the surface by its 
weight, or is forced 
down by the pressure 
of the water in the 
higher portions of the 
porous sand, until it escapes as a spring at A. A somewhat simi- 
lar spring is shown in Fig. 63. Here a broken, fractured rock 
rests on an inclined impervious rock. Springs of this class are 
generally small. 

(2) Fissure springs, where the water issues from fissures either in 
faulted rocks, or at other breaks in the rocks. Where such fissures 

penetrate the strata to 
great depths they may 
form the points of dis- 
charge for the escape 
of the subterranean 
water from basins of 
Fig. 64.-Fissure Spring. considerable area. 

Consequently, fissure springs are usually large. If, as in Fig. 
64, a pervious, water-logged stratum, A A, is situated between two 
layers of impervious rock, C C and D D, and faulted as shown, 




-A Hill-side Spring. 




DRAINAGE. 



131 



the fissure at F F, will determine the location of a spring ; for, the 
water contained within the porous strata, prevented from either 
rising or sinking by the impervious rock, will descend, until it 
reaches the fissure, and immediately rise through the fissure to the 
surface and emerge at S, as a spring. 

(3) Artesian Springs or Wells. — In basin-shaped regions, where 
porous, water-logged strata are contained between parallel, imper- 
vious strata, if the upper impervious strata are broken naturally by 
fissures, somewhat in the manner of fissure springs, or are purposely 
bored by man, the waters will escape through the openings by reason 
of the pressure of the water in the higher parts of the reservoir. 
They are usually called artesian springs or wells, and differ from 
ordinary wells in that their waters are discharged by the pressure 
of the water in the reservoir, thus rendering punaping unnecessary. 
They are, therefore, true springs. 




Fig. 65.— Artesian Spring. 



If, for example, as in Fig. 65, A A, represents a pervious, water- 
logged stratum, lying between two impervious strata, and a boring 
be made at C B, the water will issue in a jet, but not so high as the 
line A C, on account of friction and air resistance. 

Artesian wells have been sunk to great depths, and it is a significant fact that 
the temperature of the issuing waters is always proportional to the depth, show- 
ing, for every 55 feet of descent, a nearly constant increase of 1° above the tem- 
perature of ordinary springs— viz., about 60° Fahr. In the case of the artesian 
well of Grenelle, Paris, the successful boring of which was accomplished only 
after many years of the most discouraging labor, and which reached a depth of 



132 PHYSICAL GEOGRAPHY. 

nearly 1800 feet, the temperature of the water was 82° Fahr. A well at Neusalz. 
werk, Prussia, has penetrated 2200 feet ; its temperature is 91° Fahr. 

181. Classification of Springs. — Springs are conveniently 
arranged in different classes according to peculiarities in the size, 
shape, and depth of their reservoirs, and the nature of the mineral 
substances composing the strata over which the waters flow, or in 
which they collect. 

The Reservoirs of springs are the places where the waters that 
sink into the ground collect. Reservoirs are usually merely porous 
strata, such as beds of sand or gravel, which lie between impervious 
layers of clay or hard rock. The water collects in the spaces be- 
tween the particles of sand or gravel. 

182. Size of Reservoir. — When the reservoir is large and the 
rainfall sufficiently great, the spring is constant; when small, the 
spring is temporary. 

Constant Springs are those which flow continually, and which 
are but little afiected in the volume of their discharge even by 
long-continued droughts. 

Temporary Springs are those which flow only for a short time 
after wet weather, drying up on the appearance of even moderate 
droughts. 

Since the volume of water discharged by some springs is very 
considerable, we must infer that their reservoirs are of great size. 
Very large springs probably receive the drainage from many square 
miles of surface. 

Springs are common on the shores of the ocean. Their waters are fresh 
because the outflow of the fresh water from the land into the sea prevents the 
inflow of the salt water. This is the case even on coral islands, where the height 
of the land is but ten or twelve feet above the sea. A comparatively shallow 
well, on such islands, usually yields fresh water, derived, of course, from the 
rainfall. 

183. Depth of Reservoir. — According to the distance the reser- 
voir is situated below the surface of the earth, springs are divided 
into Cold, and Hot or Thermal. 

184. Cold Springs are those whose temperature does not 



DRAINAGE. 133 

exceed 60° Fahr. Their waters are sometimes much colder than 
this. 

Very cold springs owe their low temperatures to the sources 
whence they draw their supplies. In mountainous districts these 
can generally be traced to the melting of huge snow-fields, or masses 
of ice called glaciers. The temperature in such cases is nearly that 
of ordinary ice-water. 

The reservoirs of all springs the temperature of whose waters 
ranges from 50° to 60° are usually near the surface. They are 
cooler than surface waters, because they are shielded from the 
sun. 

The temperature of springs of this kind is but slightly affected by changes in 
the temperature of the outer air. Since the reservoirs of ordinary springs are 
shielded from the hot air in summer, and from the cold air in winter, their 
waters are colder than river-water in summer, and warmer than river-water 
in winter. Their waters average, in their temperature, that of the strata over 
which they flow in their subterranean courses. 

The mean annual temperature of the strata over which the waters 
flow may be ascertained by plunging a thermometer into the water 
aa it comes out of the spring. 

185. Hot or Thermal Spring's range in temperature from 60° 
Fahr. to the boiling-point. In geysers the temperature of the water, 
far down in the tube, is considerably above the boiling-point at the 
surface. 

Hot springs which occur in the neighborhood of active volcanoes 
owe their high temperature to beds of recently ejected lava situated 
in the vicinity of their reservoirs. 

Hot springs, however, are common in regions distant from volcanic 
disturbance. In such cases their high temperature must be attrib- 
uted to the distance the water sinks below the earth's surface, the 
heat being derived from the interior. Hot springs are common in 
regions where the strata are disturbed, and fractures are numerous, 
since their waters are apt to come up frohi great depths. Some hot 
springs may owe their high temperature to the oxidation of sulphides, 
or to some other chemical action. 



134 



PHYSICAL GEOGRAPHY. 





186. Geysers are boiling springs which, at intervals more or less 
regular, shoot out huge columns of water with great violence. The 

jets of water sometimes 
reach a height of more 
than 200 feet. 

The geyser issues from 
the summit of a conical hil- 
lock of silicious material de- 
posited by the water. A 
broad, shallow basin usually 
surmounts the hillock and 
forms the mouth of a deep, 
funnel-shaped tube. The 
sides of both tube and basin 
are lined with a smooth in- 
crustation of silica. In the 
Great Geyser of Iceland, 
the basin is 52 feet wide 
and the tube 75 feet deep. 

Both the tube and basin 
are the work of the spring, 
being deposited from the silica contained in the highly heated waters. It is 
only when the tube has reached a certain depth that the spring becomes a true 
geyser. When the depth becomes too great, the geyser eruptions cease, the 
waters forcing their way through the walls of the tube to some lower level. 
Hence, in all geyser regions, numerous deserted geyser-tubes and simple ther- 
mal springs occur. 

The waters of some geyser regions are caicareous. in sv".ch cases the tube of 
the geyser is, of course, formed of limestone. 

187. Bunsen's Theory of Geysers. — Bunsen explains the cause of geyser 
eruptions as follows : The heat of the yolcanic strata, through which the geyser- 
tube extends, causes the water which fills it to become highly heated. The water 
at the bottom of the tube, having to sustain the pressure of that above it, gradu- 
ally acquires a temperature far above the boiling-point at the surface. The tem- 
perature of the water in the tube will, therefore, decrease from the bottom to the 
surface. 

If now, when the tube is filled, the water, near the middle, is brought to its 
boiling temperature, the steam thus formed momentarily lifts the water in the 
upper part of the tube, when the water in the lower part, released from its press- 
ure, bursts into steam and forcibly ejects the contents of the tube. 

Bunsen succeeded in lowering a thermometer into the tube of the Great 
Geyser in Iceland just before an eruption. At the depth of 72 feet he found the 



Fig. 66.— Geyser in Eruption. 



DRAINAGE. 



135 



temperature of the water to be 261° Fahr., or 49° 
point. 



above tbe ordinary boiling- 



188. Geyser Regions. — There are three extensive geyser regions : 

(1) In Iceland, in the south-western part of the island, where over 
one hundred geysers occur in a limited area. 

(2) In New Zealand, about the centre of the northern island, 
where, near the active volcano Tongariro, over one thousand mud 
springs, hot springs, and geysers burst from the ground. 

(3) In Yellowstone National Park, in Wyoming, where numerous 
large geysers and Lot springs occur, mostly near the head-waters of 
the Madison and Yellowstone Rivers, at heights in some places as 
great as 8000 feet above the sea-level. Here the boiling-point of the 
water at the surface of the geysers, owing to the diminished atmos- 
pheric pressure, is as low as about 200° Fahr. 

A small geyser region is found in California, near San Francisco. 

189. Nature of the 
Mineral Substances 
forming- the Reser- 
voir. — The subterra- 
nean waters dissolve 
various mineral mat- 
ters either from the 
strata over which they 
flow, or from their res- 
ervoirs ; this is espe- 
cially true of thermal 
springs, owing to the 
greater solvent powers 
of the heated waters. 

The waters of mineral 
springs usually contain a number of mineral substances. Mineral 
springs are divided into various classes according to the predomina- 
ting material; viz., 

(1) Calcareous springs are those whose waters contain lime in 
solution. 




-Calcareous Deposits, Yellowstone 
National Park. 



136 PHYSICAL GEOGRAPHY. 

Thermal waters, charged with carbonic acid, usually contain large quantities of 
lime, which they have dissolved from subterranean strata. On reaching the sur- 
face the waters cool and part with some of their carbonic acid, and deposit layer 
after layer of hard limestone, called travertine. In this way immense quantities 
of lime-stone are brought to the surface from great depths, leaving huge subter- 
ranean caverns. 

In portions of Tuscany, Italy, beds of travertine occur more than 250 feet 
thick. 

Besides the stalactitic and stalagmitic deposits of lime-stone in caverns, the 
highly charged calcareous waters descending the surface slopes of the hills in por- 
tions of the Yellowstone Park have deposited the lime in a series of parapets at 
different heights, forming basins, filled with water which drips or flows to lower 
levels. Such deposits are shown in Fig. 67. 

(2) Silicious springs are those whose waters contain silica. 
(B) Sulphurous springs are those whose waters contain sulphuretted 
hydrogen and various metallic sulphides or sulphates. 

Sulphurous springs are found in Baden ; near Vienna ; and in Virginia. 

(4) Chalybeate springs are those whose waters contain iron. 

(5) Salt springs or brines are those whose waters contain common 

salt. 

The springs of Halle, in the Alps of Salzburg, yield 15,000 tons of salt an- 
nually. The artesian well of Neusalzwerk, Prussia, yields about 28,000 tons 
annually. In the United States the springs of Salina and Syracuse are among 
the most important. The water in the springs of Salina is ten times Salter than 
ocean-water. The salt is obtained from these springs by the evaporation of the 
water. 

(6) Acidulous springs are those whose waters contain large quan- 
tities of carbonic acid gas, as the Seltzer springs in Germany, and 
those of Vichy in France. 



CHAPTER III. 

Rivers. 

190. Definitions. — The water that issues from the ground aa 
springs ; that which is derived from the melting of ice or snow ; or 
that which drains directly from the surface after rainfall, runs down 



RIVERS. 137 

the slopes of the land and collects in the depressions formed by the 
intersection of the slopes, forming rills or rivulets, which, at last, 
combine in larger streams called rivers. 

The source of a river is the place where it rises ; the mouth, the 
place where it empties ; the channel, the depression through which 
it flows. Rivers usually rise in mountains, where the rainfall is 
greater than elsewhere, and where vast beds of snow and ice occur. 

Since the downward motion of a river is caused by the inclination of its chan- 
nel from the source to the mouth, a correct idea of the general inclination of any 
country can be obtained by a careful study of a map in which the directions of 
the rivers are represented. In studying the various river-systems the student 
should endeavor to obtain in this way clear ideas of the general directions of the 
continental slopes. 

The River-system is the main stream, with all its tributaries and 
branches. 

The Basin is the entire area of land which drains into the river- 
system. 

The Water-shed is the ridge or elevation which separates two op- 
posite slopes. The streams flow in opposite directions from the 
water-shed. 

The Velocity of a river depends on the inclination or pitch of the 
channel, and the volume or depth of the water. 

191. River Courses or Tracts. — A river, from its source to its 
mouth, may be divided into three courses or tracts: 

(1) The upper or mountain course or tract ; 

(2) The middle or valley course or tract ; 

(3) The lower or plains course or tract. 

192. The Upper or Mountain Course of a river is the part 
which is situated in the mountainous or hilly country near its source. 
Here the river has a high velocity, and its channel is characterized 
by sharp , sudden turns, alternating with long, straight courses, 
and is comparatively free from fine debris. In the upper course 
erosion occurs almost entirely along the bottom of the channel, so 
that the river runs between steep, and sometimes almost vertical, 
banks. In this way river-valleys are formed. In the upper and middle 
courses rapids and waterfalls occur. 





a 








a 




\ 


\} 


el 




1 




1 


,sV 


2 




2 




3 
4 




3 






4 



138 PHYSICAL GEOGRAPHY. 

Rapids and Waterfalls. — -During the erosion of the channel, where 
harder rocks occur in the bed of the stream, the softer strata, imme- 
diately adjoining them down stream, are rapidly worn away, and the 
obstruction becomes at last the head of a waterfall. The height 
grows rapidly from the 'increased force of the falling water, and con- 
tinues until stopped by some similar obstruction below. 

Thus, suppose a a, Fig. 68, is the bed of a river, the. direction of flow of which 
is shown by the arrow. The softer rock being worn away more rapidly, the bed 

reaches the level, 1, 1. 
A fall, and consequent 
increase in the velocity 
of the river, soon causes 
the level of the bed to 
reach 2, 2, 3, 3, and 4, 4, 
successively. At the same 
time the falling water 
eats away the vertical 
Fig. 68.— Erosion of Waterfall. "^^11 of the precipice, 

causing the waterfall to 
move up stream. The water then cuts the precipice away in steps, at 5, 6, 7, thus 
changing the fall into cascades. These are finally worn away, as shown at 8, 
changing the cascades to rapids, when, finally, the fall disappears entirely, or the 
erosion of the hard rock is completed. Waterfalls, therefore, near the middle 
course of a river, indicate a young stream. 

The waterfalls which occur near the source of a river in the mountainous 
region have a different origin. Here a lofty precipice may be cut out from a 
single block. Unlike the waterfalls just described, they indicate a very old 
channel ; i. e., are the final result of long-continued erosion. 

When the water falls perpendicularly — that is, when it does not 
slip or slide — it forms a waterfall or catar<tct ; in all other cases of 
swift descent it forms rapids. 

The grandest falls in the world, those of the Niagara, are 160 feet high. Though 
greatly inferior to many others in height, yet the volume of their water is so great 
that they surpass all others in grandeur. The Victoria Falls of the Zambezi in 
Africa nearly equal in volume those of the Niagara. Their height is 360 feet. 

The highest falls in the world are those of the Yosemite, in California. Two 
projecting ledges break the sheet into three falls, whose total height exceeds 2000 
feet. One of the highest falls in Europe is the Staubbach or Dust-brook, in the 
valley of the Lauterbriinnen in Switzerland. The water makes one sheer fall 
of 959 feet, and is lost in a sheet of mist before it reaches the groxmd. 



RIVERS. 



139 



Waterfalls may also be due to the draining of a lake. Many waterfalls were 
caused toward the close of the glacial epoch during the withdrawal of the ice 
sheet. 

193. The Middle or Valley Course extends from where the 
river emerges from the 
mountainous or hilly dis- 
tricts to the low plains 
near the mouth. The 
channel is wide, and con- 
tains coarse gravel and 
small boulders. The ero- 
sion of the bottom of the 
channel is insignificant, 
but at the sides, especially 
during freshets, the river 
undermines its banks, and 
thus widens its valley. 
Here the river is divided 
into two distinct portions : 
the river-channel proper 
and the alluvial flats or 
flood-grounds. 

194. The Lower or 
Plains Course extends 
from the middle course 
to the mouth. The fall 
is slight, and the velocity small. The channel is filled with fine silt 
or gravel, except in swifter portions, where coarse gravel may occur. 

195. Chang-es in River-courses. — During floods, when the velocity and 
eroding power are greatly increased, extensive changes often occur in river- 
courses. After the floods have subsided the water is found running through 
new channels, its old ones being either completely fllled with deposits of mud, 
or occupied by slender streams. Along the Mississippi these partially deserted 
channels are called bayous, and, in places, widen out into large lakes (see Fig. 
70). The Eed liiver appears to have formerly emptied into the Mexican Gulf 
through a separate channel. In the basins of the Amazon, the Ganges, and the 
Po, the old deserted channels are numerous on both banks of the streams. 




Fig. 69.— The Falls of Niagara. 



140 PHYSICAL QEOGBAPHY. 

196. River Mouths. — A wide, open river mouth is called an 
Estuary; the accumulation of mud or sand which occurs in the 
mouths of certain rivers is called a Delta. 

197. Inundations. — During certain seasons of the year, the 
amount of water drained into the river-channel is greater than it 
can discharge ; it then overflows its banks, and inundates the sur- 
rounding country. 

Inundations of rivers are caused — 

(1) By excessive rainfall ; 

(2) By periodical rains ; 

(3) By the melting of ice and snow. 

In the tropics, where the rainfall is more or less periodical, the inundations 
of the rivers are also periodical. The melting of the ice and snow, which occurs 
regularly at the beginning of the warm weather, also causes periodical inunda- 
tions. The Nile rises annually on account of the periodical rainfall of its upper 
sources ; the Mississippi semi-annually, once from the melting of snow, and once 
from the winter rainfall. 

Where both the area of the river-basin and the rainfall in inches are known, 
experience permits of a calculation, by means of which the probable time and 
extent of rise of water in a river can be approximately predicted. In times of 
heavy rainfall, the Weather Bureau of the United States is enabled to predict 
the probable rise of the important rivers. 

Influence of the Destruction of the Forests on Inundations. — When 
the forests are removed from a large portion of a river-basin, the rains are no 
longer absorbed quietly by the ground, but drain rapidly off its surface into the 
river-channels, and thus in a short time the entire precipitation is poured into 
the main channel, causing an overflow. It is from this cause that the disastrous 
effects of otherwise harmless storms are produced. The inundations are most 
intensified by this cause in the early spring, when the ice and snow begin to 
melt. The destructive effects of the floods are increased by masses of floating 
ice, which, becoming gorged in shallow places in the stream, back up the waters 
above. The increased frequency of inundations in certain parts of the United 
States is, to a great extent, to be attributed to the rapid destruction of the forests. 

198. The Quantity of Water Discharged by a River 
depends principally — 

(1) On the size of its basin ; 

(2) On the amount of its rainfall. 

199. Age of Rivers. — Like most physical features of the earth, 



RIVERS. 141 

river-systems pass through various stages of development. They 
manifest youth, maturity, and old age. 

(1) Immature or Young River-systems. — Such are the rivers that 
drain a recently uplifted district. The main rivers occupy the 
trough of the district, and the branches drain the slopes of the 
ridges. Depressions in the troughs are first filled by the main 
stream, thus forming lake-systems. The presence, therefore, of 
extended lakes in any river-system is a sign of the youth of the 
basin it drains. Examples of such youthful or immature drainage 
is seen in the lake-system of the St. Lawrence and of the great 
African lakes. In matured rivers the lakes are absent and no falls 
remain, since no marked inequalities exist in the river bed. In 
young rivers waterfalls are common, 

(2) Matured River-systems. — As the age of the river-system 
increases, erosion cuts away the land at the outlet of its lakes, thus 
draining the lake-basins ; the waterfalls eat back their precipices 
until the falls have disappeared. The river has then developed its 
tributary streams, receives its full load of sediment, and has adjusted 
its grade or inclination so as to give it a velocity just sufl[icient to 
carry its silt to its outlet. The river is then said to be graded, and 
has reached maturity. 

(3) Old Rivers. — As erosion continues, the river at last reaches 
old age. Under the combined influence of weathering and erosion 
the hills have nearly disappeared, the river has reduced its drainage 
basin to a peneplain, the load in the river decreases, becomes finer 
and finer, and the stream moves slowly to the outlet. 

No matter what may be the age of a river, so far as its develop- 
ment is concerned, it may be caused to begin its work anew, if its 
basin be uplifted further above the sea-level. In this case the river 
is said to be rejuvenated or revived. 

200. Changes Produced by Depression or Elevation of 
River-basins. — Changes in level of the surface of the river-basin 
result in marked changes in the character of its drainage, and con- 
sequently in its river-system. 

(1) Depression of River-basin ; Dismembered Rivers. — Where a 



142 PHYSICAL OEOGRAPHY. 

river-system suffers a depression of its basin near its mouth at the 
ocean, an estuary or bay is formed, and the tributary rivers dis- 
charge into the ocean as separate systems. This is the case with the 
rivers of Virginia and Maryland, that now empty into Chesapeake 
Bay. Such rivers are said to be dismembered. 

(2) Elevation of River-basins. — A number of primarily inde- 
pendent streams, on their way to the sea, across the newly formed 
surface of a coastal plain, formed by the uplift of a shallow ocean 
bed, may unite in a single stream. Such rivers are called engrafted 
rivers. It is in this way that some of the largest river-systems in 
the world have been formed. The Mississippi has received as 
engrafted streams the White, the Arkansas, the Red, and the 
Tennessee Rivers. So, also, have many of the great rivers of Bra- 
zil been engrafted on the mighty Amazon. 

201. The Transporting" Po"wer of a River increases as the 
sixth power of its velocity. Doubling its velocity, therefore, enables 
it to transport particles sixty-four times heavier. The transporting 
power will vary with the inclination of the channel ; with an 
increase in the volume of its water ; and with the size of the parti- 
cles of its load — the smaller the size of the particles, the greater the 
transporting power of the river. 

The transporting power of a river is often greatly aided by ice. 



CHAPTER IV. 

The Work of Rivers. 

202. Work of Rivers. — Rivers are ceaselessly at work carrying 
from the upper to the lower courses in the channel, or to its banks, 
the rock waste derived from weathering; or the worn, eroded mate- 
rial derived from the wear of the rock. Valleys are thus formed 
miles in width and hundreds of feet in depth. The material trans- 
ported by the river consists of boulders, gravel, sand, and fine mud. 
When in a finely divided state this material is called detritxis or silt. 
This material constitutes the river's load. 



140 IGO 180 160 140 120 100 80 




^\ 



ANTARCTIC CIRCLE 



■~^A 



HYDROGRAPHICAL MAP 

SHOWING THE 

OCEANIC BASINS, AREAS 

AND 

KIVER SYSTEMS 

OF THE EAETH 



N 



T 



R 



C 



120 Longitude 140 East from 160 Greepwich 180 



140 120 



60 80 



IOC 120 




I 



c 



REFERENCES 

]ATLANTIC SYSTEM fe | INDIAN SYSTEM 

PACIFIC SYSTEM I' | ARCTIC SYSTEM 

INLAND SYSTEM | | OCEAN DEPTHS 

(Darkest blue indicates |;renlesl depH.) 



o 



c 



E 



siitt&i 



N 



West 40 from 20 Greenwich Longitude 20 East 40 from 60 Greenwich 



THE WORK OF RIVERS. 143 

The amount of silt transported by rivers is almost incredible. According to 
the careful estimates of Ilumphreys and Abbot, the silt brought down every 
year by the Mississippi and throvpn into the Mexican Gulf, if collected in one 
place, would cover a field one square mile in area to the depth of 268 feet. 

203. Invisible Load of Rivers. — Besides the rivers' visible load 

of waste, silt, or detritus, there is also an invisible load consisting of 

dissolved mineral matter. 

According to Eussell, the Hudson carries daily to the sea 183 tons of dissolved 
mineral matter. The Mississippi discharges yearly into the Gulf of Mexico 
113,000,000 tons of dissolved mineral matter. 

204. Transporting- Power and Deposition of Rivers Influ- 
enced by Changes of Level in the Earth's Surface. — Since the 
transporting power of a river depends on its velocity, any change in 
level that affects the velocity necessarily influences its transporting 
power. Since repeated changes of level have occurred in practi- 
cally all portions of the earth's surface, this influence on the trans- 
porting power and deposition of rivers must have been very 
marked. 

205. Deposition of Silt. — Since the eroded mineral matter is 
heavier than water, it will settle in all parts of the river course. It 
will, however, remain for a more or less extended tiaie in those 
places only where the velocity of the river is comparatively slight. 
Tbese places are as follows : 

(1) In the channel of the river ; 

(2) On the banks, over the alluvial flats or flood-grounds ; 

(3) At the mouth ; 

(4) Along the coast near the mouth. 

206. In the Channel. — In rivers that traverse great plains, the 
inclination near the mouth is slight, and the diminished velocity 
allows the material to accumulate in the channel, thus raising the 
general level of the stream. 

When the rivers traverse settled districts, the inhabitants are compelled to 
erect huge river-walls to prevent the flooding of the adjacent lands ; and, in 
some places, the channel has been filled to such an extent that the ordinary 
level of the river is higher than that of the plains along its banks. 

The levees or banks of the Mississippi are of this nature. On the level plain 
of Lombardy the surface of the Po, in some places, is higher than the tops of 



144 



PHYSICAL GEOGRAPHY. 



the neighboring houses. When floods occur in such districts, the breaking of a 
levee, or river-wall, is attended by much loss. 

207. Alluvial Cones and Fans. — Where a river suddenly 
passes from a precipitous gorge on a mountain and enters a valley, 
the sudden and excessive change in grade causes most of its load 
to be deposited in the channel at the foot of the gorge. The con- 
ical deposit thus formed is called, from its shape, an alluvial cone or 
fan. Such piles are frequently several thousands of feet high, with 
bases of from three to iive miles in radius. Alluvial fans and cones 
are found especially in arid regions, where the rainfall occurs only 
during limited seasons. 

208. Rafts. — Drift timber, thrown into the stream by the undermining of 
the banks, is common in rivers that traverse wooded districts. Portions of such 
timber, becoming imbedded in shallow parts of the channel, form obstructions 

which prevent the passage of 
floating timber during subse- 
quent floods. The impedi- 
ment so formed checks the 
velocity of the stream, and 
mud deposits occur between 
the trees. Such accumula- 
tions are called rafts. The 
raft of the Red River, previ- 
ous to its removal, was thir- 
teen miles in length. 

209. On the Alluvial 
Plats or Flood-grounds. 
— The low flat plains on the 
sides of the river, which 
are formed by the erosion 
of the banks in the mid- 
dle and lower courses, 
are covered by the water, 
when the river overflows 




Fig. 70.— Alluvial Flats of the Mississippi. 

jShowing deserted courses and fluviatile islands 

and lakes.) 



its banks. In the shallow water over these parts, the velocity of the 
water is slight, and the silt is deposited, thus forming rich alluvial 
plains. 



THE WORK OF RIVERS. 145 

In large rivers the flood-grounds often attain considerable size. In the Mis- 
sissippi at Vicksburg the width of the alluvial plain is over 60 miles. 

In the lower courses of a river, the velocity being slight, com- 
paratively small obstacles suffice to turn the waters from their course. 
The river-channel is, therefore, characterized by wide bends or curves, 
called meanders. At the bend of a river the main current is directed 
against one of the banks, where rapid erosion takes place, the eroded 
material accumulating lower down the river, in the bed of the stream, 
where the velocity is slight. The river is thus continually dam- 
ming up portions of its old channel and cutting new ones. 

The rapid excavation of these portions of the alluvial plain is 
favored by the loose materials which compose it. Sometimes the 
river cuts a new channel across the narrow neck of a bend, part of 
its waters running through the old channel and part through the new. 
In this way fluviatile islands are formed. One of the channels is 
sometimes separated from the other by a deposition of mud or sand. 
The water fills the old channel by soaking through the soil, and thus 
fluviatile lakes are formed. Numerous fluviatile lakes occur near 
the banks of the Lower Mississippi and the Red River. 

210. Ferrel's La-w Applied to River Courses. — Under the 
influence of the earth's rotation, a river, in the Northern Hemisphere, 
flowing north or south, tends to corrode its right bank more than its 
left, since, if flowing poleward, its tendency is to be deflected toward 
the east, and, if flowing toward the equator, to be deflected toward 
the west ; similarly, in the Southern Hemisphere, rivers tend to cor- 
rode their left banks more than their right. 

211. River Terraces. — The river, after filling its valley with silt in the form 
of a broad, alluvial plain, may change its action and begin cutting away its plain. 
In this way, as the river successively deepens its channel, portions of the old 
plain are left as terraces. The changes in the river's action are due to successive 
changes in level, to changes in the amount of silt or waste in the stream, or to 
changes in the depth of the lower river course or channel. 

212. At the Mouth. — Delta Formations. — When rivers empty 
into parts of the ocean devoid of marked currents, or into lakes, the 
silt or detritus is deposited very much in the shape of alluvial 
fans or cones. Such deposits are called deltas, from their general 

10 



146 



PHYSICAL GEOGRAPHY. 



resemblance to the shape of the Greek letter Delta [A). When 
strong currents exist, the material is carried beyond the river mouth 
and deposited in bars or flats along the shores. 
Deltas are divided by Russell into two classes : 

(1) Deltas formed by streams of high grade and, consequently, 
great velocity. Here the load consists of mixed detritus of various 
sizes, which, on reaching the ocean or lake is sorted, the coarser and 
heavier particles falling at once to the bottom, the finer sand and silt 
being carried further out, while the very fine silt is carried still fur- 
ther away and forms a mud sheet over a fairly extended area. Three 
marked regions are thus produced. 

(2) Deltas formed by streams of low grade and, consequently, slight 
velocity, such as the Mississippi, the Yukon, the Mackenzie, the Nile, 
and the Ganges. Here the load consists of fine silt, and the three 
divisions of the preceding class are wanting, the fine silt settling in 
broad deposits with somewhat indefinite borders, forming shoals and 
new land. Here the river discharges through numerous branches, 
each branch tending to build up a delta at its mouth. In low-grade 
deltas the main stream discharges through a number of separate 
branches, or distributaries. 

The Delta of the Mississippi is the largest in the Western Continent. Its 
entire area is about 12,300 square miles, although but two-thirds of it are perma- 
nently above the water, the 
remainder being a sea- 
marsh. It begins a little 
below the mouth of the Eed 
Eiver. The stream cuts 
through the delta in one 
main channel but, near the 
extreme end of the delta, 
forms several mouths. On 
all sides of the main stream, 
numerous smaller streams 
force their way into the 
Gulf of Mexico through the 
soft material. 

Fig. 71.— Delta of the Mississippi (Dana). The Delta of the Nile, 

at its outlet into the Medi- 
terranean, occupies an area of nearly 9000 square miles. A large portion of the 




THE WORK OF RIVERS. 



147 



sediment of the river is deposited over the flood-grounds during inundations. 
The fertility of the land is largely dependent on these deposits. 

The Delta of the Ganges and the Brahmapootra, in the Bay of Bengal, 
is considerably larger than the Delta of the Nile. Betvreen the Hoogly and the 
main branch of the Ganges, numerous streams force their way between countless 
islands, called the Sunderbunds, inhabited by tigers and crocodiles. The Po, the 
Rhone, the Rhine, and the Danube in Europe, the Tigris, the Euphrates, the Yang-tse- 
Kiang and Hoang-Ho in Asia, and the Senegal and the Zambezi in Africa, have 
extensive deltas. 



213. Dro"wned Rivers. — The sinking or depression of coastal 
plains, traversed by rivers, permits tlie sea to enter their valleys, thus 
changing them into bays and estuaries, bordered by numerous 
islands, where the higher lands rise above the waters. Such rivers 
are common on the Atlantic and St. 

Lawrence slopes in North America. 
The estuaries of the Chesapeake and 
Delaware Bays are examples. The 
St. Lawrence formerly discharged at 
a point eastward of the present loca- 
tion of Nova Scotia. The Hudson 
formerly discharged some 70 miles 
east of Long Island. The rugged 
coast of Maine, with its numerous 
islands, capes, bays, etc., is due to 
the partial depression of a rough 
surface below the sea level. Here 
the rough surface is partially due to 
hills and ridges whose origin is to be 
traced to glacial deposition. 

Golden Gate, Puget Sound and its 
numerous islands, and much of the 
coast northward to Alaska, have 
been formed, in a similar manner, by 

subsidence of river-systems, traversing a region modified by glacial 
Action. 

214. Along the Coast, near the Mouth. — Pluvio-marine 




Fig. 



72. — Fluvio-marine For- 
mations. 



148 



PHYSICAL GEOGRAPHY. 



Formations are deposits of silt and sand that form along the coast 
near and opposite the mouths of rivers, under the combined action 
of the river-current and the tides of the ocean. A har or sand-spit 
is formed at some little distance from the mouth of the river, where 
the outflowing river-current and the inflowing tide tend to neutralize 
each other. 

An example of this formation is shown in Fig. 72, where sand- 
bars or spits have formed along the coasts of North Carolina ofl" the 
mouths of the drowned rivers, thus separating the sounds from the 
ocean. The shallow waters of the sounds, being thus protected from 
the scouring action of the waves, are slowly filled up by the silt 
from the rivers, and may, in course of time, be gradually changed 
into swamps, and the coast-line be moved further seaward. 

215. Development of a River System. — The drainage systems 
undergo profound changes through the erosion of their valleys. In 
a newly emerged surface, such as that shown in Fig. 73, from Scott, 
a slope, whose escarpments are indicated by the shaded lines, is 





Fig. 73.— First Stage (DeLaparent). Fig. 74.— Second Stage (DeLaparent), 



drained by five streams a, c, e,/, and g, which flow down the trans- 
verse valleys, and into the longitudinal valley which occupies the 
trough formed by the intersection of opposite slopes. Should one 
etreara, say c, receive more water than the others, it will erode and 
deepen its channel more rapidly, and thus its tributaries will acquire 



DRAINAGE SYSTEMS. 149 

a greater fall. Side branches form and tap neighboring streams e 
and a, which then find through the invading stream a readier escape 
from their waters above the point of tapping. In this manner c 
has captured or beheaded a and e, as shown in Fig. 74. Some of these 
streams, as e, may be changed in direction, flowing into the captured 
stream, thus leaving at h, a wind-gap. The point where the stream 
cuts through a ridge becomes a water-gap, as at m. 



olOio 



CHAPTER V. 

Drainage Systems. 

216. Continental Drainage is dependent on the position of the 
mountain-systems and the direction of their slopes. The mountain- 
ridges or peaks, or the high plateaus, form the water-sheds. In 
some cases, from the slopes of a single peak or plateau, the water 
drains in different directions into distinct river-systems, and empties 
into different oceans. 

217. North America. — The central plain of North America is 
drained by four large river-systems : the Mackenzie into the Arctic 
Ocean ; the Saskatchewan and the Nelson into Hudson Bay ; the 
St. Lawrence into the Gulf of St. Lawrence; and the Mississippi 
into the Gulf of Mexico. The basin of the Mississippi occupies 
the long slopes of the Rocky Mountains and the Appalachians. 
The Missouri and the Ohio are the principal tributaries of the 
Mississippi. An uplift of the coastal plain bordering on the Mexi- 
can Gulf has resulted in engrafting on the Mississippi system the 
Red, the Tennessee, the White, and the Arkansas. 

Numerous streams descend the eastern slopes of the Appalachian 
Mountains into the Atlantic. 

Owing to the position of the predominant system, the streams 
which empty into the Pacific are comparatively small. The prin- 
cipal large streams are the Yukon, the Columbia, and the Colorado. 



150 PHYSICAL GEOGRAPHY. 

There are several remarkable isolated water-sheds or drainage-centres in North 
America. These are — 

(1) In the central part of the Eocky Mountains, where the land drains in 
different directions into the systems of the Mississippi, the Columbia, and the 
Colorado Eivers. 

(2) In the northern part of the Eocky Mountains, where the drainage is 
received by the systems of the Yukon, the Mackenzie, and the Saskatchewan 
Eivers. 

218. South America resembles North America in its drainage 
systems. The long, gentle slopes of the Andes, and those of the 
systems of Brazil and of Guiana, are occupied at their intersections 
by the three great river-systems of the continent : that of the Ori- 
noco, in the north ; that of the Amazon, near the centre ; and that 
of the La Plata, in the south. Nearly the entire continent is 
drained by these rivers and their tributaries into the basin of the 
Atlantic. 

The Pacific receives no considerable streams. Only impetuous 
mountain-torrents are found. 

The Magdalena, which drains north, corresponds to the Mackenzie ; the Ori- 
noco and the Amazon, which drain east, to the Nelson and the St. Lawrence; 
and the La Plata, which drains south, to the Mississippi. 

219. Europe forms an exception to the other continents as 
regards its drainage. Though some of its large rivers rise in its 
predominant mountain-system, yet the majority rise in the incon- 
siderable elevations of the Valdai Hills. The Alps are drained by 
four large rivers — the Rhone, the Rhine, the Danube, and the Po. 
These all have large deltas. 

The Oreat Low Plain of Europe is drained toward the north and 
west by the Petchora and Dwina into the Arctic ; by the Duna, the 
Niemen, the Vistula, and the Oder into the Baltic ; and by the Elbe 
and the Weser into the North Sea. It is drained toward the south 
and east by the Ural and the Volga into the inland basin of the 
Caspian; and by the 7)o??,, the Dnieper, zx\di the Dniester into the 
Sea of Azov and the Black Sea. 

All the peninsulas have streams traversing them. The Seine, the Loire, and 
the Garonne from France, and the Douro, the Tagus, and the Gaudiana from 



DRAINAGE SYSTEMS. 151 

Spain and Portugal, empty into the Atlantic. The Ehro from Spain, and the Po 
from Italy, empty into the Mediterranean. 

220. Asia possesses the most extensive inland drainage of all the 
continents. The plateaus are surrounded by lofty mountains ; the 
rainfall is scant over the plateaus, and the waters can find no out- 
let to the sea except by overflowing mountain barriers. The outer 
slopes, however, are drained by some of the largest rivers in the 
world. 

The Great Northern Plain drains into the Arctic, mainly through 
the Lena, the Yenisei, and the Ohe. 

The Eastern Slopes drain into the Pacific through the Amoor, the 
Hoang-Ho, the Yang-tse-Kiang, and the Cambodia. 

The Southern Slopes drain into the Indian Ocean through the 
Irrawaddy, the Brahmapootra, the Ganges, the Indus, the Tigris, and 
the Euphrates. 

The principal drainage-centre in Asia is the Plateau of Thibet, from which de- 
scend the Hoang-Ho, the Yang-tse-Kiang, the Cambodia, the Irrawaddy, the 
Ganges, the Brahmapootra, and the Indus. 

221. Africa, being low in the interior, with high mountain-walls 
on her borders, is characterized, like the Americas, by the union of 
her smaller river-systems into a few large streams, which drain nearly 
the entire continent. These embrace the Nile, emptying into the 
Mediterranean ; the Zambezi, into the Indian Ocean ; and the 
Orange, the Congo, the Niger, and the Senegal, into the Atlantic. 

222. Australia. — The Murray, which drains the south-eastern 
part of the continent into the Indian Ocean, is the only considerable 
stream. 

223. Principal Oceanic Systems. — A careful study of the river- 
basins of the different oceans discloses the following fact : 

The Atlantic and Arctic Oceans receive the waters of nearly all the 
large river-systems of the world. 

The cause of this is as follows : The predominant systems being 
situated nearest the deepest ocean, the long, gentle slopes descend 
toward the smaller, shallower oceans (the Atlantic and the Arctic), 
which thus receive the greatest drainage. 



152 PHYSICAL GEOGRAPHY. 

CHAPTER VI. 

Lakes. 

224. Lakes are bodies of water that occupy depressions in the 
general drainage level of the land. They form part of either the 
oceanic or the inland drainage systems. The waters of lakes empty- 
ing into the ocean are fresh; those having no connection with the 
ocean are salt. 

Lakes are but transitory features of the earth's surface. The rivers connected 
with lake systems tend both to fill the lake-beds by the deposit of sediment at 
the river inlets into the lake, and to erode or cut down their outlets, and thus 
discharge the lake waters. Sometimes the lakes disappear because they are filled 
up by sediment deposited by the rivers or blown in by the winds. As the lakes 
gradually fill in this way, they are changed into swamps and, finally, into level, 
fertile plains. More frequently, however, the river cuts down the outlet and 
thus destroys the lake by discharging its waters. 

The depressions to which lakes owe their formation are due to a 
variety of causes, which serve as an excellent basis for their division 
into different classes. 

(1) Lakes of New Land-areas. — In comparatively level country, 
such as is frequently found in land recently raised above the sea- 
level, the small inequalities in the land are filled with the surface 
water in the form of shallow ponds or lakes. Such lakes are numer- 
ous in the United States in Florida, along the coast of the Gulf of 
Mexico, and in parts of the South Atlantic coast, all of these being 
recently elevated land areas. Since these shallow lakes are apt to 
become swamps they are sometimes called marsh lakes. 

(2) Lakes in the Lower Course of a River, especially in the Delta 
District. — Here the level nature of the surface is favorable to the 
formation of shallow lakes and swamps. Where the deltas are 
formed by streams of low grade, the natural levees formed along the 
branching outlets, or distributaries, are broken through during floods, 
and their low areas left as shallow lakes. Lakes Pontchartrain and 
Borgne, in Louisiana, are of this type. Changes in river courses. 



LAKES. 163 

as we have seen, are apt to form ox-how lakes in the abandoned 
meanders. 

(3) Lagoons or Sea-shore Lakes. — The coves or bays so numerous 
on certain sea-coasts may be shut off from the ocean by the forma- 
tion of sand-bars, and thus converted into lakes. Such lakes are 
numerous along the Atlantic shores of the United States. 

(4) Glacial Lakes. — A glaciated district ; l. e., a district once oc- 
cupied by a glacier, is characterized by numerous lakes. Of such 
an origin are the lakes in the northern part of the United States 
and the Dominion of Canada. These lakes generally occupy long, 
narrow basins. They include the lakes of Wisconsin and Minne- 
sota, the finger lakes of New York, the Adirondack lakes, and the 
abundant lakes of New England. Such, too, are the many lakes of 
Sweden. 

The basins of glacial lakes have been cut or grooved in the hard rock by the 
movement of the glacial masses with their imbedded rocks ; or, they have been 
formed during the retreat of the ice by deposits laid across streams, thus damming 
them up and forming lake-basins of their channels ; or, the general drainage 
surface has been deranged by irregular deposits derived in various vrays by the 
glacier or its streams. 

(5) Lake-systems in Regions of Depression and Elevation. — When 
river-systems traverse regions in which more or less sudden changes 
of level may occur, as in growing mountain districts, the river valley 
may be depressed in one place and elevated in another further down 
stream. In such cases the depressed part is occupied by a lake that 
discharges into the river below. Such a cause has produced many 
of the larger lakes in the Alps. 

(6) Lake-hasins due to Earthquakes. — The permanent changes of 
level sometimes caused by earthquakes, resulting in an uneven sur- 
face, frequently give rise to lakes by a collection of the surface 
waters in the lowest depressions. The lakes of the sunken country 
in south-eastern Missouri are of this character. 

(7) Lake-hasins due to Landslides and Lava Streams. — When a 
landslide, or a lava stream, deposits material across a valley, the 
stream draining the valley fills up the depression, forming a lake 
which is discharged over its lowest margin. 



154 



PHYSICAL GEOGRAPHY. 



(8) Play a Lakes. — Where rivers flow through a level country in 
interior basins, where the rainfall is scanty, and large lakes are 
absent, the water, during times of flood, spreads out in a temporary 
lake. Silt is deposited on this area, forming an extremely level plain. 
Such a lake district is called a playa. Black Rock Desert in Nevada 
is an example. 

(9) Climatic Changes Indicated by Deserted Lake-basins. — Many 
regions, now arid, were formerly well watered. In the Sahara 

desert, the existence of 
former large rivers is 
proved by the numer- 
ous wadies or dry river 
valleys. Great SaltLake 
in Utah was formerly 
a much larger lake, 
called in honor of the 
explorer of its original 
outlines, Lake Bonne- 
ville. Another such 
lake, Lahontan, for- 
merly occupied the 
western part of Nevada. 
Humboldt Lake now occupies a portion of its former area. 




Fig. 75.— Lakes Bonneville and Lahontan. 




Fig. 76.— Depth of Lakes. 



225. Lake-systems with Oceanic Drainage. — North Amer- 
ica contains the most extensive lake-system in the world. This 



LAKES. 



155 




Fig. 77.— A Mountain Lake, 8000 feet Mgh. 



region surrounds Hudson Bay, and drains into the Arctic through 
the Mackenzie ; into Hudson Bay through the Saskatchewan ; or 
into the Atlantic 
through the St. Law- 
rence. To it belong 
the Great Lakes — Supe- 
rior, Michigan, Huron, 
Erie, and Ontario — 
embracing a combined 
area of nearly 100,000 
square miles — and the 
numerous lakes of Brit- 
ish America. 

The Great Lakes occupy 
one of the most remarkable 
series of depressions in the 
general land-surface of the 

world. Lake Superior, though some 600 feet above the level of the ocean, 
reaches, in its greatest depths, far below the ocean's surface, being over 400 feet 
below the general level of the Atlantic. - 

Athabasca, Great Slave, and Great Bear Lakes drain into the Arctic through 
the Mackenzie ; Lake Winnepeg, into Hudson Bay through the Nelson; and the 
Great Lakes, into the Atlantic through the St. Lawrence. 

Europe contains two extensive systems of fresh-water lakes. 
The larger region is in Low Europe, and surrounds the Baltic Sea 
and its branches. The smaller region is in the Alps in High 
Europe. 

Africa contains an extensive system of lakes west of the predomi- 
nant system. Victoria Nyanza and Albert Nyanza, which drain 
into the Nile ; Lake Tanganyika, which drains into the Living- 
stone or the Congo ; and Lake Nyassa, which drains into the Zam- 
bezi, are the principal lakes. 

The remaining continents contain but few large fresh-water lakes. 
In South America we find Lake Maracaybo, with brackish water 
from its vicinity to the sea ; and in Asia, Lake Baikal. 

North America. — The largest inland drainage-system is in the Great 
Basin, containing Great Salt, Walker, Pyramid, and Oioen Lakes. 



156 PHYSICAL GEOGRAPHY. 

South America. — The largest region of inland drainage includes 
the plateau of Bolivia. 

Europe and Asia contain a vast region of inland drainage extend- 
ing from the Valdai Hills eastward to the Great Kinghan Mountains, 
embracing most of the Asiatic plateaus. 

The region contains Lake Elton in Eussia, and the Caspian and Aral Seas. The 
combined area of the last two is 175,000 square railes. 

Africa contains Lake Tchad in the Soudan and Lake Ngami in 
Southern Africa. 

Australia contains Lakes Eyre, Torrens, and Gairdner. 

226. Lake-systems with Inland Drainage are intimately con- 
nected with inland river-systems. The water of such lakes is salt. 

227. The Dead Sea in Syria is remarkable for the quantity of its saline ingre- 
dients. In every one hundred pounds of its waters there are over twenty-six 
pounds, or more than one-fourth, of various saline ingredients. A still salter lake 
is Lake Van in Eastern Turkey. It contains 33 per cent, of saline ingredients. 

228. Salt Lakes are characteristic of regions with scanty rain- 
fall and great evaporation. They are formed in two ways : 

(1) By the isolation of a part of the ocean, such as by the forma- 
tion of a sand-bar, or by an elevation of a part of the sea-bottom. 

(2) B}- the continued concentration of river water in lakes with 
no outlet. The lakes then lose fresh water only by evaporation, and, 
since all river water contains saline substances, the lakes must be 
continually increasing in saltiness. 

In either case the rainfall must be scanty, since, otherwise, the level of the 
lake would rise until the lake discharged itself over the lowest point, and the 
water would become fresh. 

Precipitation of Dissolved Saline Substances. — When a body of salty water begins 
to deposit its various dissolved salts, the least soluble is thrown down first ; for 
example, in the case of salt lakes formed by the shutting off of parts of the 
ocean, the gypsum, or sulphate of lime, is first thrown down, and afterward common 
salt, which is far more soluble than gypsum. 

229. Marshes, Swamps, Morasses, and Bogs. — Where the 
drainage is so incomplete that the water cannot readily run off, 
swamps, marshes, morasses, and bogs are formed. Generally, the first 
stage is to form a very shallow marsh-lake. Then vegetable matter 



LAKES. 157 

begins to collect, and the swamp is converted into a marsh. When 
vegetable matter is kept moist it does not decay as completely as it 
would if exposed to dry air. Instead of merely passing off as 
gaseous products, it is slowly changed into a blackish slime which 
accumulates and forms a swamp. 

But in addition to this action, which is common to all vegetable matter, there 
Are several varieties of a plant called the sphagnum, a kind of water moss which 
greatly aids swamp formation. This plant has long, thread-like roots which die 
as they sink in the water, hut continue growing at their upper extremity. The 
dead rootlets accumulating, at last fill up the lake and convert it into a morass 
or bog. Sometimes only the surface of a lake will be covered with a closely 
entwined mass of the sphagnum plant, thus making a quagmire. Lives are often 
lost owing to the treacherous nature of the covering. 

Peat bogs are formed in a similar way by the collection of vege- 
tation in damp places. Peat appears to require for its best forma- 
tion both cold and moisture, though it is sometimes found in warm 
climates. 

By means of the above processes lake basins are converted into 
alluvial or lacustrine plains, traversed by the streams that formerly 
fed the lakes. These streams eventually cut their way through the 
alluvial plains, forming terraced valleys and completely removing 
all traces of the former lakes. 

230. Some Characteristics of Fresh-water Lakes. — Fresh- 
water lakes have a comparatively short life. They are but tempo- 
rary features of the surface drainage systems. There are two causes 
which tend to obliterate them : 

(1) The filling up of their basins by sedimentation from their 
inflowing streams. 

(2) The outflowing streams tending to cut down their outlets and 
thus gradually drain the lake. 

231. Utility of Lakes. — By offering extended basins into which the rivers, 
when swollen, can disgorge themselves, lakes greatly diminish the destructive 
effects of inundations in their outlet streams, often checking them entirely. 
They afford extended surfaces for evaporation, and, acting as settling reservoirs 
collecting the finer sediment of the rivers, their beds form fertile plains when 
deserted by their waters. They both store up and purify water, and their presence 
often aids in regulating climate. Large lakes furnish the best of inland water- 
ways, promoting navigation. The smaller ones are sources of food supply, favor- 
ite summer resorts, and add greatly to tlie beauty of landscape. 



158 PHYSICAL OEOQBAPHY. 



SYLLABUS. 

Water is formed by tlie union of oxygen and hydrogen. It is a solid at and 
below 32° Fahr., and a liquid from 32° to 212° Fahr. It passes off as vapor at all 
temperatures. 

Large bodies of water moderate tbe extremes of temperature, because water 
takes in more heat while warming, and gives out more heat in cooling, than any 
other common substance. 

After a pound of water has been cooled to 32° Fahr., it has still 142 heat-units 
to lose before it can freeze. After a pound of ice has been warmed to .32° Fahr., 
it has still 142 heat-units to gain before it can melt. Therefore, both freezing 
and melting are gradual processes. 

The rains cleanse the surface of the earth and purify the atmosphere. 

Water is necessary for the existence of life. It forms the main food of both 
animals and plants. 

The atmospheric waters are drained into the ocean either by surface or by 
subterranean drainage. 

Springs are: (1) Hillside springs; (2) Fisstu'e springs; (3) Artesian springs or 
wells. 

According to the size of their reservoirs, springs are either constant or tempo- 
rary. When their reservoirs are superficial, springs are cold ; when deep-seated, 
they are Iwt or thermal. 

Springs whose waters are moderately cold have their reservoirs near the sur- 
face. Their lower temperature is due to their waters being shielded from the 
sun. 

Hot or thermal springs owe their high temperature to the heat they receive 
from the interior of the earth. 

Geysers are boiling springs, which, at irregular intervals, discharge huge col- 
umns of water with great violence. The most extensive geyser regions are those 
of Iceland, New Zealand, and Wyoming. 

Calcareous springs contain lime ; silicious, silica ; sulphurous, sulphuretted 
hydrogen and metallic sulphides or sulphates ; chalybeate, iron ; brines, common 
salt ; acidulous, carbonic acid. 

Elvers are fed both by surface and subterranean drainage. 

The main stream with all its tributaries and branches is called the river-system. 
The territory drained into the river-system is called the river-basin. The ridge 
or elevation separating opposite slopes is called the water-shed. 

In the upper or mountain courses of rivers erosion occurs mainly on the bottom 
of the channel ; in the middle or valley courses, at the sides. 

Inundations are caused by excessive rain and by the melting of ice and snow. 

The destruction of forests, by increasing the rapidity of surface drainage, 
increases the violence of floods. Lakes along river-courses decrease their violence 
by allowing the torrents to discharge or spread out their waters. 

Eiver-systems are : (1) Immature; (2) Mature; (3) Old. 



SYLLABUS. 159 

In the lower courses of rivers rich alluvial plains are formed by the erosion 
of the banks and the subsequent deposition of the silt during inundations. 

The depression of a river-basin may cause the tributary rivers of a system to 
discharge into the ocean as separate systems. Such rivers are said to be dismem- 
bered. The elevation of a river-basin may cause several independent river- 
systems to unite in a single system. Such rivers are said to be engrafted. 

Elvers are ceaselessly at work transporting boulders, gravel, sand, mud, and 
silt from their upper to their lower courses. The boulders, gravel, sand, and fint 
mud transported by a river from its upper to its lower courses constitute its load. 
The dissolved mineral matter constitutes its invisible load. 

When a river suddenly passes from a steep mountain gorge and enters a valley, 
it deposits its load at the foot of the gorge in an alluvial fan or cone. 

The earth's rotation causes rivers in the Northern Hemisphere, if flowing north 
or south, to tend to corrode their right banks more than their left, and in the 
Southern Hemisphere, to tend to corrode the left banks more than the right. 

Silt may accumulate: (1) In the channel; (2) Along the banks; (3) At the 
mouth ; and (4) Along the coast near the mouth. 

When rivers empty into lakes, or into the ocean, where tides and currents are 
absent or feeble, the eroded material, or silt, accumulates at the mouths of the 
rivers in masses termed deltas. 

The following rivers have extensive delta-formations, viz., the Mississippi, 
Ehine, Rhone, Po, Danube, Hoang-Ho, Yang-tse-Kiang, Ganges, Brahmapootra, 
Indus, Nile, Tigris, Euphrates, and the Zambesi. 

The central plain of North America is drained north into the Arctic Ocean 
through the Mackenzie ; east, into the Atlantic through the Nelson and the St. 
Lawrence ; and south, into the Gulf of Mexico through the Mississippi. Numerous 
streams drain the eastern slopes of the Appalachian Mountains into the Atlantic. 

The central plain of South America is drained north into the Caribbean Sea 
through the Magdalena; east, into the Atlantic through the Orinoco and the 
Amazon; and south, into the Atlantic through the Eio de la Plata. 

The rivers draining the predominant mountain-system of Europe are the 
Ehone, Ehine, Danube, and Po ; those draining the great low plain rise either in 
the Valdai Hills or on the northern slopes of the predominant mountain-system. 

Asia possesses the most extended system of inland drainage of the continents. 
Africa is drained by the union of her smaller rivers into a few large streams. 

In Australia, the only large stream is the Murray, which drains the south 
eastern part of the continent. 

The Atlantic and the Arctic Oceans drain about three-fourths of the conti- 
nental waters. 

Lakes are : (1) Lakes of new land-areas ; (2) Delta lakes ; (3) Lagoon or sea- 
shore lakes ; (4) Glacial lakes ; (5) Lakes of regions of depression or elevation ■ 
(6) Earthquake lakes ; (7) Lakes due to land-slides and lava-streams ; (8) Playa 
lakes. 

The largest systems of fresh-water lakes occur in North America and Africa. 



160 PHYSICAL GEOGRAPHY. 

The Great Lakes of North America occupy remarkable depressions In the con- 
tinent. 

Salt lakes are formed : (1) By the isolation of a part of the ocean ; (2) By the 
continued concentration of river-water in lakes without an outlet. 

Marshes, swamps, morasses, and bogs are due to incomplete drainage. 

^><^o, 



REVIEW QUESTIONS* 

What effect has the temperature of the maximum density of water on the 
freezing of large bodies of fresh water? 

What is the composition of water ? 

Enumerate some of the physical properties which enable water to play so 
important a part in the economy of the earth. 

How do large bodies of water moderate the extremes of heat and cold? 

Why are freezing and melting necessarily gradual processes? 

State some of the useful results produced by rain. 

Explain the cause of deserts. 

Define subterranean drainage. Surface drainage. 

Explain the origin of fissure springs ; of hillside springs ; of artesian springs. 

What is the probable cause of the high temperature of hot springs ? 

How may the probable depth of the reservoir of an artesian spring be ascer- 
tained from the temperature of its waters ? 

What are geysers? Explain the cause of their eruption. What is the origin 
of the tube and basin of a geyser? Name the three largest geyser regions of the 
world. 

What is travertine ? How is it formed ? 

How are the precipices of waterfalls caused? In what courses of a river are 
they most common? Name the highest waterfall in the world. Name the 
grandest. 

Distinguish between an estuary and a delta. 

How does the destruction of forests increase the severity of inundations? 

Upon what does the quantity of water in a river depend ? 

What do you understand by an immature river-system ? By a matured river- 
system? By an old river-system? State the characteristics of each. 

Distinguish between the visible and the invisible load of a river. 

In what difierent portions of a stream may the silt or detritus be deposited ? 

Into what two classes are deltas divided by Eussell ? 

Define dismembered river. Engrafted river. Drowned river. Ca-ptured or 
beheaded river; wind-gap; water-gap. 

Explain the formation of an alluvial fan or cone. What are rafts? How are 
they caused ? 

Explain the formation of fluviatile islands and lakes. 



SYLLABUS. 161 

State Ferrel's law as applied to river courses. 

Name some of the most extensive delta-formations in North America. In 
Europe. In Asia. In Africa. 

What is the probable origin of the swamp-lands of the Atlantic seaboard ? 

In what respects do the drainage systems of North America resemble those 
of South America? 

How were the depressions now occupied by lakes formed? 

Explain the causes of the saltness of some inland waters. 

Name the principal systems of inland drainage of the world. 

Describe the formation of marshes, swamps, morasses, bogs, and peat bogs. 

Give a short life history of a fresh-water lake. 

o-y-pS^OO 

MAP QUESTIONS* 

Which two oceans drain the largest proportion of the areas of the continents? 

Name the important rivers which drain into the Atlantic from North America. 
From South America. From Europe. From Africa. 

Name the important rivers which drain into the Pacific from North America. 
From Asia. 

Name the important rivers which drain into the Indian Ocean from Africa. 
From Asia. From Australia. 

Name the important systems of inland drainage in North America. In South 
America. In Europe and Asia. In Africa. In Australia. 

Name an important steppe lake and river in each of the continents. 

Name the large rivers which drain the predominant mountain-system of Asia. 
Of Europe. Of Africa. Of North America. Of South America. Of Australia. 

Describe the fresh-water lake-region of North America. Of South America. 
Of Europe. Of Africa. 

Name the Atlantic rivers which have large deltas. The Pacific riversu Tli» 
Indian rivers. 
11 



162 PHYSICAL .GEQOBAPHY. 

SECTION II. 
OCEANIC WATERS. 

— o^r«io<' — 

CHAPTER I. 

The Ocean. 

232. Composition. — The water of the ocean contains a number 
of various saline ingredients, which give it a bitter taste and render 
it heavier than fresh water in the proportion of 1.027 to 1. 

Every hundred pounds of ocean-water contains about three and 
one-third pounds of various saline ingredients. 

CWoride of sodium, or common salt, cUoride and sulphate of magnesium, 
sulphate and carbonate of lime, chloride of potassium, and bromide of magne- 
sium, are the principal saline ingredients. 

233. Origin of the Saltness of the Ocean. — The rivers are constantly dis- 
solving from their channels large quantities of mineral matters, and pouring 
them into the ocean. In this way immense quantities of mineral ingredients 
have been dissolved out from the crust, and thrown into the ocean. 

The ocean issaltest at about the latitude of the tropics, where the evaporation 
exceeds the rainfall ; where the rainfull exceeds the evaporation, the water is 
sligttly fresher than at the equator. 

In inland seas, like the Mediterranean or the Eed Sea, which, though con- 
nected with the ocean, yet lose much more of their waters by evaporation than 
by outflow, the proportion of salt is slightly greater than in the ocean. In such 
cases a current generally flows into the sea from the ocean. In colder latitudes, 
inland seas, like the Baltic, receiving the waters of large rivers, contain rathei 
less salt than the open sea, and as a rule, a current flows from them into the ocean. 

234. Color. — Though transparent and colorless in small quanti- 
ties, yet in large masses the color of sea-water is a deep blue. The 
same is true of fresh water. Over limited portions of the ocean the 
waters are sometimes of a reddish or a greenish hue, from the pres- 
ence of numerous minute organisms. 

Sometimes a pale light or phosphorescence, visible only at night 
and due to the presence of animalculse, appears where the air comes 



THE OCEAN. 163 

into contact with the water, as in the wake of a vessel, or on the 
crests of the waves. 

235. Temperature. — The temperature of the surface water varies 
from about 80° F. in the tropics, to nearly 27° F. (its freezing-point), 
in the polar regions. Between these extremes, the temperature varies 
irregularly with the latitude, owing to the ocean currents. 

In the deep ocean, the temperature of the water on the floor of the 
ocean is very nearly constant ; viz., near the temperature of the 
maximum density of ocean-water, which is nearly the same as its 
freezing-point ; for, ocean-water, unlike fresh water, continues to 
contract and grow denser as it is cooled, until near its freezing- 
point. Unlike the land, the ocean is not subject to sudden changes 
in temperature, either during the day or year. The daily range is 
not much greater than about 3° F., and the annual range is not 
much greater than 15° F. 

The nearly constant low temperature of the deep ocean water in all latitudes 
is readily understood. As the water in the polar region reaches the temperature 
of its greatest density, it sinks to the bottom and spreads over the floor of the 
ocean in all latitudes, so that, except where stirred by ocean currents, the entire 
bottom of the ocean is covered by a layer of dense, heavy water, whose tempera^ 
ture is nearly constant. 

The upper limit of this line of invariable temperature varies with the latitude. 
Near the equator, where the waters are heated to great depths, it is found at about 
10,000 feet below the surface. Toward the poles, it comes nearer the surface, 
reaching it at about Lat. 60°, from which point it again sinks, being found at Lat. 
70° at about 4500 feet below the surface. 

The salts dissolved in ocean-water lower its freezing-point. Ordinary ocean- 
water freezes at about 27° F. T\Tiere the ocean is less salt its freezing-point is 
higher ; when it is more salt its freezing-point is lower. 

236. Ocean Ice. — Ice formed from ocean-watcf is comparatively 
fresh, nearly all the salt being separated as the ice forms. The salt 
thus thrown out is dissolved by the water below the ice, which, be- 
coming Salter, has its freezing-point lowered. The water below the 
ice may, therefore, have a temperature lower than that at which the 
surface water freezes, and yet remain liquid. 

Ice formed from ocean-water expands a little on freezing and, 
therefore, floats. The ice which forms on the ocean in the polar 



164 



PHYSICAL GEOGRAPHY. 



regions collects in what are called, when in extensive unbroken areas, 
^ee-fields or ice-sheets. This ice may form to the depth of from 3 to 7 




-^""^^^^v^ss-'^wm^^m^Sim 



Big. 78. — Ice-pack (Joliu M. Justice). 

feet in onewinter. Detached masses floating about are called ice-floes. 
Ice-floes, when drifted or blown together, or against the shore, become 
piled up in irregular masses called ice-packs. The ice that forms 
along the shore in a narrow, nearly level shelf, is called the ice-foot. 

237. Shape of the Ocean's Bed. — The oceanic waters occupy a 
vast sunken area whose mean depth is nearly two and a half miles. 
The true bed of the ocean is assumed as beginning at the 100-fathom 
line, where the water is 600 feet deep. Anything shallower than 
this is taken as the submerged continental border, or, as it is gen- 
erally called, the continental shelf. 

A continental shelf, 75 or 100 miles in breadth, extends along the 
eastern coast of North America, from Newfoundland to Florida, and 
around the shore of the Mexican Gulf and part of Central America. 
The British Isles and the Asiatic and Australasian Island chains 
rest on continental shelves that lie on the border of Asia and Aus- 



THE OCEAN. 165 

tralia. The continental shelf on the Pacific borders is compara- 
tively narrow. In cold climates these continental shelves form the 
world's best fishing-grounds. Beyond the limits of the continental 
shelves, that is, on the true continental borders, the waters suddenly 
deepen, and the true oceanic basin begins. 

The floor of the ocean is by no means uniformly level or flat, 
although it is far from being so diversified as the surface of the 
land. Careful soundings show that it has vast plateaus and plains, 
and that it extends for great distances in gentle undulations and slopes 
called floors. The reason for this is evident. Erosion, so common 
on the land, is practically absent in the deep ocean, which, constantly 
receiving sediment from the rivers, or from the remains of countless 
animals, is gradually having its smaller irregularities filled up. It 
has, however, submerged mou.itain-ranges, the summits of which form 
island chains. Moreover, there are many places where there are deep 
and abrupt slopes ; these are called cauldrons, when the depressions 
are wide and deep with sloping sides ; furrows, when they are nar- 
row with deep sides ; and troughs, when they are narrow and shallow. 
Any relatively wide elevation is called a hanh, and any horizontal 
bank is called a shelf. A shoal is any place where the water is less 
than 5 fathoms (30 feet) in depth. 

The western half of the Pacific and Atlantic, and the eastern half 
of the Indian Ocean, contain nearly all the very deep depressions. 
A general idea of the varying depths of the ocean may be obtained 
from a study of the map of the Oceanic Areas. 

238. Depth of the Ocean. — The depth of the ocean is deter- 
mined by means of the sounding-line. The sounding-line for deep- 
sea measurements consists of a thin steel wire, attached to a sounding 
instrument, weighted by a heavy iron ball B, arranged so as to detach 
the ball on its striking the bottom. The ball surrounds a brass tube 
T, called the water-bottle, which is open while descending, but is closed 
automatically as the line is hauled in. The arrangement of the parts 
is shown in Fig. 79. The water-bottle is employed for obtaining 
specimens of deep-sea water. 

The deepest trench in the seas is off Mindanao, in the Pacific, 32,088 feet deep. 
Seven other Pacific soundings show depths greater than 30,000 feet. Nare's 



166 



PHYSICAL GEOGRAPHY. 




Deep, to the north of the West Indies in the Atlantic, is 27,972 feet. The 
greatest depth yet found in the Indian Ocean is 21,968 feet. Thus the maximum 
depth is about six miles and the average a little over two miles. 

In order to examine the character of the ocean beds, dredges, 
drawn by wire ropes, are employed. 
To these ropes, nets are sometimes at- 
tached, in order to secure chance speci- 
mens of deep-sea life. 

239. The Oceanic Areas. — The 
ocean forms one continuous body of 
water, but for purposes of description 
and study it is usually divided into 
five smaller bodies : the Pacific, At- 
lantic, Indian, Arctic, and Antarctic 
Oceans. The last two are separated 
from the preceding by the polar cir- 
cles ; the others are separated mainly 
by the continents. As the continents 
do not extend to the Antarctic Circle, 
the meridians of Cape Horn, Cape of 
Good Hope, and South Cape in Tas- 
mania, are taken as the ocean boun- 
daries south of these points, as shown 
in the map of the oceanic areas and river-systems. 

The following table gives the relative size of the oceanic areas : 
The Pacific occupies about \ the entire water-area. 
" Atlantic " " i " " 

" Indian " " \ 

" Antarctic " " tt " " 

" Arctic " " ■s'g " " 

240. Articulation of Land and Water. — The indentations of 
the oceans, or the lines of junction between the water and the land, 
may be arranged under four heads : 

(1) Inland or Mediterranean Seas, or those surrounded by 
a nearly continuous or unbroken land-border ; as the Gulf of 
Mexico, Hudson Bay, the Baltic, and the Mediterranean, in the 




—Deep-sea Sounding 
Instruments. 



THE OCEAN. 



1d7 



A-tlantic ; the Red Sea and the Persian Gulf, in the Indian ; and 
the Gulf of California, in the Pacific. 

(2) Border Seas, or those isolated from the rest of the ocean 
by peninsulas and island chains ; as the Caribbean Sea, the Gulf 
of St. Lawrence, and the North Sea in the Atlantic ; and Bering 
Sea, the Sea of Okhotsk, the Sea of Japan, and the North and 
South China Seas, in the Pacific. 

(3) Gulfs and Bays, or broad expansions of water extending 
but a short distance into the land; as the Gulf of Guinea and 
the Bay of Biscay, in the Atlantic ; and the Bay of Bengal and 
the Arabian Sea, in the Indian. 

(4) Fiords, or deep inlets, with high rocky headlands, extending 
far into the land. 

The Atlantic Ocean is characterized by inland seas ; the Pacific, by 
border seas ; the Indian, by gulfs and bays. 

241. Ooze Deposits. — Foraminiferal Land. — The reef-forming 
coral polyps are not the only animalculse, the accumulation of whose 
bodies after death, adds to the land- 
masses of the earth. Deep-sea 
soundings show that over extended 
areas the floor of the ocean is evenly 
covered with a creamy layer of mud 
or ooze, which, like the deposits of 
the coral animalculse, is composed 
principally of carbonate of lime. 
This ooze consists almost entirely 
of microscopic skeletons of a group 
of animalculse known as Foramin- 
ifera, from the great number of per- 
forations or openings in their hard parts. These animalculse are 
so small that 1,000,000 are equal in bulk to only one cubic mch. 
As shown in Fig. 80, they are highly magnified. They appear to 
live in the layers of water near the surface, and after death, to fall 
gradually to the bottom of the sea. Soundings show the presence 
of their remains over very extended areas. 




Fig. 80. — Foraminifera. 



168 



PHYSICAL GEOGRAPHY. 



Many of the very deep parts of the ocean's bed are covered, not with fora- 
miuiferal deposits, but with a layer of red mud composed of finely-divided clay. 
Its origin is probably as follows : In very deep parts of the ocean, before the fora- 
miniferal deposits reach the bottom their lime is dissolved, and the undissolved 
parts form the deposits of fine red mud. 



CHAPTER II. 

Oceanic Movements. 

242. The Oceanic Movements may be arranged under three 

heads : waves, tides, and currents. 

Waves are swinging motions of the water, caused by the 

friction of the wind on the surface. Their height and velocity 

depend on the force of the 
wind, and the depth of the 
basin in which they occur. 
The stronger the wind, and 
the deeper the ocean, the 
higher the waves and the 
greater their velocity ; great 
waves formed in the deep 
ocean by powerful winds are 
frequently called seas. 




Fig. 81. — A Diagram of a Wave Form 
Showing the Various Parts. Note the 
White Caps on the Crests and the Forma- 
tion of Breakers in the Foreground. 



Heig-lit of Waves. — Scoresby 
measured waves in the North At- 
lantic 43 feet above the level of 
the trough. Waves have been re- 
ported in the South Atlantic, oif the Cape of Good Hope, between 50 and 60 feet 
high. Navigators have occasionally reported higher waves, but the accuracy of 
their measurements may perhaps be doubted. In the open sea, with only a 
moderate wind, the height of ordinary waves is about 6 feet. 

The distance between two successive wave-crests varies from 10 to 20 times 
their height. Waves 4 feet high have their successive crests about 40 feet apart ; 
those 33 feet high, about 500 feet apart. 




120 Longitude 140 East from 160 G.veawich 180 



SO Longitude 




West 40 from 20 Greenwich Longitude 20 East 40 from GO Greenwich 80 



OCEANIC MOVEMENTS. 169 

243. No Progressive Motion of "Water in Waves. — In wave 
motion, the water seems to be moving in the direction in which the 
wave is advancing, but this is only apparent ; light objects, floating 
on the water, rise and fall, but do not move forward with the wave. 
When the wind is high, the top of the wave is pushed forward and 
breaks, forming white caps. In shallow water, however, the water 
really advances. The forward motion of the wave is then retarded, 
so that the following waves reach it, thus increasing its height. The 
motion at the bottom is lessened, and the top curls over and breaks, 
producing what are called breakers. 

On gently sloping shores, the water which runs down the beach, after it has 
been thrown upon it by the breakers, forms, at a little distance from the shore, 
the dreaded undertow of our bathing-resorts. 

244. Force of the "Waves. — When high, and moving in the 
direction of the wind, the waves dash against any obstacle, such as 
a line of coast, with great force, and may thus cut it away and 
change the coast-line. This action occurs only on exposed, shelving 
coasts. The wave-motion is, in general, very feeble at 40 feet below 
the surface. The eroding action of the ocean waves is, therefore, far 
inferior to that of the continental waters. 

245. Earthquake "Waves. — Earthquakes, occurring on the floor 
of the ocean, set immense masses of water in motion, and produce 
low waves that move with a great velocity. On reaching shallow 
water the height of the wave increases often to 50 or 60 feet, so that 
the waves may cause great damage on low coasts. Such waves are 
often improperly called tidal waves. An earthquake in Southern 
Peru, in 1868, sent such a wave westward across the Pacific to New 
Zealand and Australia, north-westward to the Sandwich Islands, 
and north to the coast of Oregon. 

246. Tides are periodical risings and fallings of the water that 
succeed each other with great regularity about every six hours. 
Unlike waves, whose motion is confined mainly to the surface, tides 
aflfect the waters of the ocean from the top to the bottom. 

The rising of the water is called flood tide ; the falling, ebb tide. 
When the Avaters reach their highest and lowest points, they are 




170 PHYSICAL GEOGRAPHY. 

stationary for a few minutes. These points are called respectively 
high water and loiv water. High water occurs at any place twice 
in every 24 hours and 51 minutes. 

247. Theory of the Tides. — If the earth were uniformly cov- 
ered with a layer of water, as shown in Fig. 82, where the depth 
of the water is purposely exaggerated for clearness, the passage 
of the moon over any place, such as at A, would cause the 
water to lose its globular form, and become 
,,-' — --.^ raised or bulged at A and B, and flattened or 

lowered at D and E. In other words, the 
water would become deeper at A and B, at 
I the parts of the earth nearest and furthest 
from the moon, and shallower in all places 
at right angles to these parts, such, for exam- 
Fig. 82.-L^ar Tide. P^®' ^^ ^^ ^ ^"^ ^- ^^' "^ °^^®^ words, the 
passage of the moon over any part of the waters 
would cause high water on the parts of the earth directly under the 
moon, and low water at all parts 90° from the parts of high water. 

This deepening and shallowing of the water is caused by the 
attraction of the moon. As the moon passes over A, the water is 
drawn toward it from all sides, thus deepening the water at A, and 
rendering it shallower at D and JE. 

The cause of the deepening of the water at B, on the side furthest 
from the moon, is as follows : The solid earth being, as a whole, nearer 
the moon than the water at B, but further from it than the water 
at A, must take up a position, under the attraction of the moon, 
nearly midway between A and B, thus leaving a protuberance at 
B, nearly equal to that at A. 

High tides then, produced by the moon, occur at those points of 
the earth's surface which are cut by a straight line passing through 
the centres of the earth and the moon. Low tides are formed in 
all places 90° from these points. 

Had the earth no rotation, the tidal waves formed by the moon's 
attraction would slowly follow the moon in its motion around the 
earth. But, since by the earth's rotation, difierent parts of the sur- 



OCEANIC MOVEMENTS. 171 

face are rapidly brought under the moon, its tidal waves move rap- 
idly from one part of the ocean to another. 

Had the moon no motion around the earth, there would be two 
high tides aud two low tides in, exactly, every 24 hours. While, 
however, the earth is making one complete rotation, the moon, in 
its motion around the earth, has so far changed its position that the 
earth rotates, on the average, for some 51 minutes longer, before the 
same point again comes directly u,nder the moon ; hence, 24 hours 
and 51 minutes are necessary to complete the tides. 

Since the uniformity of the water surface is broken by the ele- 
vations of the land, the progress of the tidal wave is greatly affected 
by the size, shape, and depth of the oceanic basins, and the position 
of the continents. Owing to the obstructions offered by the conti- 
nents, and by inequalities in the bed of the ocean, a considerable 
retardation of the tidal wave is effected, so that high tide may not 
occur at a place until long after the moon has passed over it. 

248. Solar Tides. — The sun also produces a system of tidal 
waves, but owing to its greater distance from the earth, the tides thus 
produced are much smaller than those of the moon. The tide pro- 
duced by the moon is about 21 times greater than that produced by 
the sun. 

The tidal wave moves, in general, from east to west, or in a direction opposite to 
that of the rotation of the earth. The motion of so large a mass of water, thus opposed 
to the earth's rotation, must gradually diminish the axial velocity, and, eventually, 
entirely stop the rotation of the earth ; in this way an increase in the length 
of day and night should be produced ; so far, however, no increase has been de- 
tected, although astronomical observations extend backward for long periods. 
The increased axial velocity, produced by the contraction of the globe, probably 
balances the retarding influence of the tides. 

In the deep ocean, and near the mouths of rivers, the duration of the flood and 
ebb are about equal ; but in most rivers, at some distance from the mouth, the ebb 
is longer than the flood. The cause is to be found in the fact that the outflowing 
river current meets and temporarily neutralizes the inflowing flood tide, thus 
diminishing its duration, and afterward, adding its motion to the ebb, makes the 
difierence between the two still greater. 

The tidal wave often ascends a stream to a much greater elevation above the 
level of its mouth than the height of the tide at the river's mouth. In large 
rivers, like the Amazon, the tidal wave, as it advances up the river, rises nearly 
100 feet above the sea-level. 



172 PHYSICAL OEOORAPHY. 

When the tidal wave strikes the shore of a continent it is reflected, and moves 
back again into the ocean, meeting and modifying the incoming tidal wave. If 
the two waves move simultaneously in the same direction the incoming tide will 
be increased ; if they move in opposite directions, the tide will be decreased. It 
is for this reason that the tides are, at times, unusually high in some places, and 
almost entirely absent in others. Then, again, some places, such as the eastern 
coasts of Scotland and England, receive their tides by two separate waves that 
reach them by diflferent routes from the north and the south ; in some places a 
tide of double height occurs ; other places are almost without tides ; while in still 
other places, four separate and distinct periods of high water occur in every 
twenty-four hours and fifty-one minutes. 

Some of the proofs of the connection between the tides and the attraction of 
che jaoon and sun are as follows : 

(1) The interval between corresponding high tides at any place is the same as 
the interval between two successive passages of the moon over that place : 24 
hours, 51 minutes. 

(2) The tides are higher when the moon is nearer the earth. 

(3) The tides are higher when the sun and moon are simultaneously acting to 
cause high tides in the same places. 

Effects of Waves and Tides — Waves are the principal agents 
in breaking down the margin of the land and in building beaches, 
bars, and spits. They destroy sea walls, docks, and vessels by 
their force. The undertow is efficient in grinding up and removing 
rock fragments. Mariners sometimes succeed in making a space of 
relatively smooth water around a ship by pouring overboard a 
quantity of oil. This reduces the friction of the wind upon the sur- 
face so that wave motion nearly ceases. Waves furnish the power 
required to ring bells in bell-buoys, and to blow the signals of 
whistling buoys. Attempts have been made to harness their power 
so as to have them pump water to higher levels. 

Tides modify the shore line, prevent stagnation of waters in harbors, and carry 
waste out to sea. They affect navigation by enabling large vessels to penetrate 
the land by deepening shallow water near shore, in river mouths, and in wide- 
mouthed coast indentations. The movement also gives a favorable current for 
in-going and out-going vessels. Their constant action often opens inlets in reefs 
and bars. In addition tliey bring food to fixed forms of animal life, furnish 
power to tide mills and aid in the work of raising sunken ships and lowering 
or raising bridges into position. 

249. Spring and Neap Tides. — When the sun and moon act 
simultaneously, on the same hemisphere, as shown in Fig. 84, the 
tidal wave is higher than usual. The flood tides are then highest 



OCEANIC MOVEMENTS. 



173 



and the ebb tides lowest. These are called spring tides. They occur 
twice during every revolution of the moon — once at full and once 
at new moon. The highest spring tides occur a short time before 
the March and the September equinoxes, when the sun is over the 
equator. 

When, however, the sun and moon are 90° apart, or in quadra- 
ture, each produces a tide on the portion of the earth directly 
under it, diminishing that produced by the other body. High 
tide, then, occurs under the moon, while the high tide caused by the 
sun becomes, by comparison, a low tide. Such tides are called neap 




iiiiie; 




Neap Tides, 
flood and ebb moderate. 



Springr Tides, 
flood and ebb excessive. 



Fig. 84.— Position of the Earth, Moon, and Sun during Spring and Neap Tides. 



tides. During their prevalence, the flood is not very high, nor the 
ebb very low. They occur twice during each revolution of the 
moon, but are lowest about the time of the June and December 
solstices. 

The average relative height of the spring tide to that of the neap tide is about 
as 7 to 4. 

250. Birthplace of the Tidal Wave. — Although a tidal wave 
is formed in all parts of the ocean where the moon is overhead, yet 
the " Cradle of the Tides " may properly be located in the great 
southern area of the Pacific Ocean. Here the combined attraction 
of the sun and moon originate a wave, which would travel around 



174 PHYSICAL GEOGRAPHY. 

the earth due east and west, with its crests north and south ; but, 
meeting the channels of the oceans, it is forced up them toward the 
north. Its progress is accelerated in the deep basins, and retarded in 
the shallow ones. On striking the coasts of the continents, deflected 
or secondary waves move off in different directions, thus producing 
great complexity in the form of the parent wave. 

251. Co-tidal Lines. — The progress of the tidal wave, in each 
of the oceans, is best understood by tracing on a map lines connect- 
ing all places which receive the tidal wave at the same time. These 
are called co-tidal lines. The distance between two consecutive lines 
represents the time, in hours, required for the progress of the tidal 
wave. Where the wave travels rapidly, the co-tidal lines are far 
apart ; when its progress is retarded, they are crowded together. 

Since it is possible to take tlie height of the tide only on the coasts of islands 
and continents, the tracks of the co-tidal lines in the deep ocean must be, to a 
considerable extent, conjectural. 

252. The Pacific Ocean. — Twice every day a tidal wave starts 
in the south-eastern part of the Pacific Ocean, west of South Amer- 
ica, somewhere between the two heavy lines marked xii on the ^hart. 
It advances rapidly toward the north-west in the deep valley of this 
ocean, reaching Kamtchatka in about 6 hours. Toward the west, its 
progress is retarded by the shallower water and by the numerous 
islands, so that it only reaches New Zealand in about 6 hours and 
enters the Indian Ocean in about 12 hours. 

253. The Indian Ocean. — The 12-hour-old tidal wave from the 
Pacific, meets and moves along with a wave started in this ocean by 
the moon, and advances in the direction indicated by the co-tidal 
lines entering the Atlantic Ocean about 12 hours afterward. 

254. The Atlantic Ocean. — The tidal wave from the Indian 
joins two other Avaves, one formed by the moon in the Atlantic, and 
the other a deflected wave that has backed into the Atlantic from 
the Pacific. The tidal wave thus formed advances rapidly up the 
deep valley of the Atlantic, reaching Newfoundland 12 hours after- 
ward, or 36 hours after it started in the Pacific. It then advances 
rather less rapidly toward the north-east, reaching the Loffoden 



OCEANIC MOVEMENTS. 



175 




176 PHYSICAL GEOGRAPHY. 

Islands 12 hours afterward, or 48 hours after leaving its starting- 
place in the Pacific. 

255. Tides in Inland Seas and Lakes are very small and, 
consequently, difiicult to detect. In the Mediterranean Sea the 
tides on the coasts average about 18 inches. Observations on Lake 
Michigan at Chicago show that the tides have a range of 1.5 inches 
for the neap tide, and 3 inches for the spring tide. 

Movements in lake waters, due to the prolonged action of strong winds, are 
far more pronounced. A gale from the north has caused the waters of Lake 
Michigan to rise to the height of seven feet at Chicago. The waters of Lake 
Erie have been caused to fall between seven and nine feet below the normal 
level by a storm from the west, unusually high water being caused at the eastern 
end of the lake. 

256. Height of Tidal "Wave. — The tides are lowest in mid- 
ocean, where they range from two to three feet. Off the coasts of 
the continents, especially when forced up narrow, shelving bays, 
deep gulfs, or broad river mouths, they attain great heights. The 
cause of these unusual heights is evident. When the progress of 
the tidal wave is retarded, either by the contraction of the channel 
or by other causes, the following part of the wave overtakes the 
advanced part, and thus, what the wave loses in speed it gains in 
height, from the heaping up of the advancing waters. Where the 
co-tidal lines, therefore, are crowded together on the chart, high tides 
are indicated; for example, the Arabian Sea and Bay of Bengal, 
the North and South China Seas, the eastern coasts of Patagonia, 
the Bay of Fundy, the English Channel, and the Irish Sea have 
very high tides. 

Near the heads of the Persian Gulf and the China Sea, the tides sometimes rise 
about 36 feet. At the mouth of the Severn, the spring tides rise from 45 to 48 
feet ; on the southern coast of the English Channel, 50 feet ; and in the Bay of 
Fundy, near the head, the spring tides, aided by favoring winds, sometimes reach 
70 feet, and, occasionally, even 100 feet. 

257. Other Tidal Phenomena. 

The Bore or Eager.— On entering the estuary of a river, the volume of 
whose discharge is considerable, the onward progress of the tidal wave is 
checked ; but, piling up its waters, the incoming tide at last overcomes the 
resistance of the stream, and advances rapidly in several huge waves. The 



OCEAN CURRENTS. Ill 

tides of the Hoogly, tlie Elbe, the Weser, the Yang-tse-Kiang, and the Amazon 
are examples. In the latter river the wave is said to rise from 30 to 50 feet. 

Races and "Whirlpools. — When ccnsiderable diiferences of level are caused 
by the tides, in parts of the oceaa separated by narrow channels, the waters, in 
their effort to regain their equilibrium, move with great velocity, producing what 
are called races. At times several races meet each other obliquely, thus produc- 
ing whirlpools. Xear the Channel Islands, and off the northern coasts of Scot- 
land, races are numerous. The Maelstrom, off the coasts of Norway, is an 
instance of a whirlpool, though the motion of the waters is not exactly a whirl- 
ing one. The main phenomenon is a rapid motion of the waters, alternately 
backward and forward, caused by the conflict of tidal currents off the Loffoden 
Islands. 

«>>*:o« 

CHAPTER III. 
Ocean Currents. 

258. Constant Ocean Currents. — Besides tidal currents, the 
waters of the ocean are disturbed to great depths by currents moving 
with considerable regularity to and from the equatorial and polar 
regions, thus producing a constant interchange of their waters. 
These movements are called constant currents ; their motion, unlike 
that of waves, is a real, onward movement of the water. 

It would appear that currents sweep the floor of the ocean at all depths, for 
everywhere the composition of the water is practically the same. 

Constant ocean currents resemble rivers, but are immensely broader 
and deeper. As a rule, their temperature differs considerably from 
that of the waters through which they flow. They are not confined 
to the surface, but exist, also, at great depths. They are called 
under- or counter-currents, when they flow in a direction opposite to 
that of the surface currents. 

259. Origin of Constant Ocean Currents.— Perrel's Law.— 
The principal cause of constant ocean currents is the difference in 
the density of the waters of the equatorial and polar regions aris- 
ing from their difference of temperature. 

As the waters of the polar regions lose their heat, they grow 
dense, and, sinking below the warmer, lighter waters, spread, as an 
12 



178 PHYSICAL GEOGRAPHY. 

under-current, over the entire floor of the ocean until they reach the 
equatorial regions, as is shown by the fact that a, layer of water is 
found in all parts of the deep ocean at nearly the same temperature ; 
viz., near the temperature of its greatest density. At the same time, 
the warmer, lighter water of the equatorial regions, flows, in all 
longitudes, as surface currents toward the polar regions. In this 
manner, a constant interchange is efiected between the equatorial 
and the polar waters, which, for the greater part, takes place along 
the bottom from the poles to the equatorial regions, and along the 
surface from the equatorial to the polar regions. Where the ocean 
is deep enough, the colder, denser water will be underneath and the 
warmer, lighter water on the surface. But in shallow water the cold 
currents come to the surface, displacing the warmer currents and 
deflecting them to deeper parts of the ocean. 

Were the earth uniformly covered with water and had no rotation, 
there would thus be established north and south currents in all longi- 
tudes. Were the earth uniformly covered with water and rotating, 
the waters flowing toward the equator would be deflected, both 
from the north and south polar regions, to the westward, and, unit- 
ing at the equator, would form a westward equatorial current 
sweeping around the earth. But this westward flowing water, 
would, in all longitudes, be constantly turning north and south as 
a surface current, finally moving eastward in the polar regions and 
joining the deep-seated polar currents to the equator. 

If now the continental masses be considered, it will be seen that 
they oppose the westward and eastward movements of the equatorial 
and polar currents. On reaching the shores of the continents, the 
equatorial currents are deflected in north and south branches. Their 
rate of flow is increased, on reaching the border of the ocean, on 
account of the smaller depth. By reason of the rotation of the earth 
the currents that are moving toward the poles are deflected toward 
the east, and those that are moving toward the equator are deflected 
toward the west. Besides the main interchange between the equa- 
torial and the polar regions, there is a smaller interchange efiected 
between the poles and the eastward running waters. 



OCEAN CURRENTS. 



179 



Ocean currents that are practically limited to the surface are 
called drifts; deeper currents are called streams. 

The action of the winds tends to move the surface currents in the direction in 
which the winds are blowing. This action is by some authorities regarded as the 
principal cause of ocean-currents. The winds are undoubtedly a partial cause, but 
cannot be regarded as the principal cause. Both ocean-currents and winds have 
their origin in the same causes; viz., differences of density caused by differ- 
ences of temperature. Apart from the greater deflecting effect produced on the 
ocean-currents by the interposition of the continents, and the greater disturbing 
effect produced on the aerial currents by the local differences of temperature of 
the land- and water-areas, the general directions of the ocean-currents and winds 
are the same. The winds, therefore, cannot but affect the ocean-currents, and 
are an important, indeed, perhaps, the chief factor, in producing the drift cur- 
rents. This is seen by the direction of the drifts being sometimes reversed by 
the high winds of storms, as well as by the fact, that in the Indian Ocean, the 
direction of the drifts follows the direction of the monsoons. The winds, how- 
ever, cannot produce the deep-seated polar currents, or ensure that thorough 
mixing of the water at all depths, which is shown to exist by the fact that ocean 
water at all depths has practically the same composition, and that no matter 
from how great a depth the water has been taken, it is fouiad to contain atmo- 
spheric air in solution. 

260. General Features of Constant Currents. — The following 
motions of iho. surface currents are com- 
mon to the three central oceans : 

(1) A movement of the equatorial 
waters a, a. Fig. 86, from east to west ; 

(2) Their deflection into northern 
and southern branches (h and c), on 
reaching the western borders of the 
ocean ; 

(3) A movement of the waters be- 
yond the equator from west to east 
{d, e) ; 

(4) A separation of these latter 
currents into two branches (/, g 
and A., -i), one continuing toward the poles, and the other toward 
the equator, where they join with the equatorial currents, thus com- 
pleting a circuit in the shape of a vast ellipse ; 




ia»-EquatQT. 



- Chart of Constant 
Currents. 



180 PHYSICAL GEOGRAPHY. 

(5) A flow of the Arctic waters along the western border of the 
ocean {j), and of the Antarctic along the eastern border (k). 

Since the Indian Ocean is completely closed on the north, only part of the 
above movements are observed. In the Pacific, an equatorial counter-current 
crosses the ocean from west to east. 

261. CTirrents of the Atlantic. — The Equatorial Current crosses 
the ocean, from east to west, in two branches : a south equatorial 
current, which comes from the Antarctic, and a north equatorial 
cuirent, which comes mainly from regions north of the equator. 

The North Equatorial Current crosses the ocean from east to west, 
and, separating near the Antilles, part of it enters the Caribbean 
Sea and Gulf of Mexico, and part flows north, passing east of 
the Bahamas. 

The Grulf Stream flows along the '^.astern coast of North America, 
with a velocity of from four to hv^e miles per hour, and in mid- 
ocean, between Newfoundland and Spain, divides, one branch flow- 
ing toward Norway, Spitzbergen, and Nova Zembla, the other 
flowing southward, down the coast of Africa, where it forms the 
main feeder of the North Equatorial Current. 

The South Equatorial Current, after crossing the ocean, divides into 
two branches. The northern branch flows along the northern coast 
of South America, where it adds its waters to those of the North 
Equatorial Current of the Atlantic, and aids in forming the Gulf 
Stream. The southern branch flows south along the Brazilian coast, 
and divides near Eio Janeiro, the main part flowing eastward and 
mingling with the Antarctic Current Cold currents from the Arctic 
flow down the coasts of Greenland and Labrador. A broad polar 
current sweeps from the Antarctic Ocean, and forms the main feeder 
of the South Equatorial Current, but passes in greater part eastward, 
south of Africa. 

262. Currents of the Pacific. — North and south equatorial cur- 
rents flow from east to west, and between them a smaller, less power- 
ful equatorial counter-current, from west to east. The South Equa- 
torial Current, fed by the broad Antarctic Current, is the larger of 
the two. 



OCEAN CURRENTS. 181 

The North Equatorial Current, on reaching the Philippine Islands, 
flows north-east along the Asiatic coast as the Japan Current, the 
Pacific counterpart of the Gulf Stream. At about Lat. 50° this 
flows eastwardly as the North Pacific Current, and off the shores of 
North America it returns, as the California Current, in an elliptical 
path, southerly to the North Equatorial Current, forming its main 
feeder. 

The South Equatorial Current is broken into numerous branches 
during its passage through the islands in mid-ocean. Reaching the 
Australian Continent and the neighboring archipelagoes, it sends 
small streams toward the north, but the main portion flows south, 
along the Australian coast, as the East Australian Current, when, 
flowing eastward, it merges with the cold Antarctic Current. 

The Antarctic Current moves as a broad belt of water toward 
the north-east, when, flowing up the western coast of South America, 
it turns to the west, and forms the main feeder of the South Equa- 
torial Current. A part of the Antarctic Current flows eastward, 
south of South America, and enters the Atlantic as the Gape Horn 
Current. 

A small cold current from the Arctic Ocean flows through Bering 
Strait, down the Asiatic coast. 

263. Currents of the Indian Ocean. — Only one Equatorial Cur- 
rent exists, which flows down the eastern and western coast of Mada- 
gascar, and down the African coast to Cape Agulhas, when, turning 
eastward, it merges with the Antarctic Current, and flows up the 
western coast of Australia, where it joins the Equatorial Current. 

The North Equatorial Current in this ocean is indistinct — 

(1) Because the ocean has no outlet to the north ; 

(2) Powerful seasonal winds, called the monsoons, move the waters alternately 
in different directions, as huge drift currents. 

264. Sargasso Seas. — Effects of Currents. — Near the centre 
of the elliptical movement in each of the central oceans, masses of 
sea-weed have collected where the water is least disturbed and where 
the winds are weak. These are called sargasso seas. 

(1) Ocean-currents moderate the extremes of climate by carrying 



182 PHYSICAL GEOGRAPHY. 

the warm equatorial waters to the poles, and the cold polar waters 
to the equator ; 

(2) They increase materially the speed of vessels sailing in cer- 
tain directions ; 

(3) They transport large quantities of timber to high northern 
latitudes. 

Surface currents affect the movement of icebergs and floe ice (page 245)- 
Vessels are often wrecked by collision with an iceberg, and floating ice favors 
the formation of fog, which increases the danger of collision. For these reasons, 
steamship routes across the North Atlantic vary somewhat with the season, in 
order to avoid the floating ice. Warm currents often help to cause fogs at sea 
and on land. When wind blows over a warm current it takes up a large supply 
of moisture. If it then blows over colder water, it is cooled, and some of its 
moisture is condensed, producing a fog. 

Ocean currents bring food supply to fixed marine animals, such as the coral 
polyps, and also to fish in the cool waters off Newfoundland, Norway, Alaska, 
and Japan. They transport marine animal life and plant life over enormous 
distances. 

Submarine banks are formed by sediment deposited by ocean currents. The 
Banks of Newfoundland are caused by deposits of earth and rocks carried by 
the polar currents, aided, most probably, by sediment carried by the Gulf 
Stream. The Bahama Banks are probably due to sediment carried in the Gulf 
by rivers and transported by the Gulf Stream to the banks. 

265. Life in the Ocean. — Animals and plants abound at or near the surface 
of the sea, and at the bottom where the water is shallow. Living things are 
present, but not in great numbers, at the bottom of the deep sea. The temper- 
ature, the depth, the clearness, the saltness, and the quietness or roughness of 
the water, influence the life which it contains. At the bottom animals are found 
whose bodies are full of liquid under the same pressure as the water, and these 
great pressures within balance those without. Tiie most familiar land plants 
are fixed in position, but many sea plants float. Most land animals are free to 
move about, while many of those in the sea, as polyps and barnacles, are fixed 
through most of their lives. All the great groups of animal life are represented. 
Even warm-blooded types abound in frigid waters. Fur, oil, whalebone, leather, 
coral, and sponges are sea products. The total value of food products is not 
less than $600,000,000 per year. 

SYLLABUS* 

One hundred pounds of ocean water contain about three and one-third pounds 
of various saline ingredients, the principal of which are chloride of sodium, chlo- 
ride and sulphate of magnesium, sulphate and carbonate of lime, chloride of 
potassium, and bromide of magnesium, 



SYLLABUS. 183 

The salt of the ocean is derived either from the washings of the land, or is 
dissolved out from the portions of the crust which are continually covered by 
its waters. 

The ocean is salter in those parts where the evaporation exceeds the rainfall. 
Seas in which the evaporation is greater than the rainfall are salter than the 
ocean ; those in which the rainfall exceeds the evaporation are fresher than the 
ocean. 

The bottom, or iloor, of the ocean is not so much diversified as the surface 
of the land. 

The articulation of land and water assumes four distinct forms : Inland Seas, 
Border Seas, Gulfs and Bays, and Fiords. Inland Seas characterize the Atlantic ; 
Border Seas, the Pacific; Gtdfs and Bays, the Indian Ocean; and Fiords, the Atlan- 
tic and Pacific. 

The greatest depth of the Atlantic Ocean is about 27,366 feet ; of the Pacific, 
about 31,614 feet. 

Over extended areas the floor of the ocean is uniformly covered with a creamy 
layer of mud or ooze, formed of the hard parts of the bodies of minute animal- 
culse. 

The movements of the oceanic waters may be arranged under the three heads : 
waves, tides, and currents. 

The height and velocity of a wave depend upon the force of the wind and the 
depth of the oceanic basin. 

In ordinary wave motion the water rises and falls, but does not move forward. 

Tides are the periodical risings and fallings of the water, caused by the attrac- 
tion of the sun and moon. 

The rising of the water is called flood tide ; the falling, ebb tide. 

If the earth were uniformly covered with a layer of water, two high tides 
would occur simultaneously : one on the side of the earth directly under the sun 
or moon, the other on the side farthest from the sun or moon. 

Had the moon no real motion around the earth, there would be two high and 
two low tides in exactly twenty-four hours, or the high and low tides would be 
exactly six hours apart. Owing to the rotation of the moon, 24 hours and 51 
minutes are required to complete the tides. 

Spring Tides are caused by the combined attractions of the sun and moon on 
the same portions of the earth. Neap Tides by their opposite attractions. 

The parent tidal wave is considered as originating in the great southern area 
of the Pacific Ocean. 

Co-tidal lines are lines connecting places which receive the tidal wave at the 
same time. 

When the progress of the tidal wave is retarded by the shelving coast of a 
continent, what the tide loses in speed it gains in height. 

Bores, Races, and Whirlpools are tidal phenomena. 

Ocean waters are disturbed to great depths by constant currents whicti resem- 
ble rivers., but are immensely deeper and broader. 



184 PHYSICAL GEOOBAPHY. 

The principal cause of constant ocean currents is the difference in the density 
of the waters of the equatorial and polar regions. 

The following peculiarities characterize the constant currents in the three 
central oceans : 

(1) A flow in the equatorial regions from the east to the west ; 

(2) A flow in regions beyond the equator from the west to the east;' 

(3) A division of the eastwardly flowing extra-tropical waters in mid-ocean 
into two branches, one of which flows toward the poles, and the other toward 
the equator, where it merges into the equatorial currents. 

Waves, tides, and currents either destroy the coasts by erosion, or build them 
up by the deposit of sediment. 



REVIEW QUESTIONS, 



Explain the origin of the saltness of the oceanic waters. 

What is the freezing-point of ocean water ? 

What is the daily range of temperature of the water of the ocean? The 
yearly range ? 

How is the depth of the ocean determined ? What is the greatest depth of th& 
Altantic Ocean ? Of the Pacific ? 

What are waves ? How are waves produced ? Upon what does their height 
and velocity depend ? 

How do the areas of the Pacific and Atlantic compare with each other in size? 
Of the Antarctic and Arctic? 

What proof is there that during wave. motion in deep water there is no con- 
tinued onward motion of the water? 

Distinguish between ebb and flood tides. 

Why should the moon, which is so much smaller than the sun, exert a more 
powerful influence in producing tides? 

What are spring tides? Neap tides? During what phases of the moon dc 
they each occur? 

Where does the parent tidal wave originate ? 

What are co-tidal lines ? 

Why does the tidal wave progress from east to west ? 

In what parts of the ocean will unusually high tides occur ? Why ? 

By what are races and whirlpools occasioned ? 

Explain the origin of constant ocean currents. 

What features of constant currents are common to each of the three central 
oceans ? 

Name the principal currents of the Atlantic Ocean. Of the Pacific. Of the 
Indian. 

What are sargasso seas? How are they formed ? 

What eflfect is produced by ocean currents on the extremes of climate ? 



SYLLABUS. 185 

In what manner are ocean currents useful to mankind ? 

Give an example of the destructive eifects of currents, tides, or waves. Of 
she constructive effects. 

»0>»<00 

MAP QUESTIONS. 

Point out ott the map of the river-systems the inland seas of the Atlantic \ 
of the Pacific ; of the Indian Ocean. 

Point out the border seas of the Atlantic ; of the Pacific. 

Point out the gulfs or bays of the Atlantic; of the Indian Ocean. 

Point out the principal regions of fiords. 

How many hours does it take the tidal wave to progress from Tasmania to the 
Cape of Good Hope? From Tasmania to Newfoundland? From Tasmania to 
the British Isles? (See map of the co-tidal lines.) 

In what parts of the Atlantic does the tidal influence progress most rapidly? 

If the velocity of any kind of wave motion in water increases with the depth 
of the basin, what parts of the Atlantic appear to be the deepest? What portions 
of the Pacific ? What portions of the Indian Ocean ? 

Trace on the map of the ocean currents the motion of the Antarctic currents 
in each of the three central oceans. 

Where is the Cape Horn current ? Is it hot or cold ? What points of rescn 
blance exist between the north and south equatorial currents in the Atlantic and 
Pacific Oceans? 

Trace the progress of the Gulf Stream. 

What points of resemblance exist between the Gulf Stream and the Japan 
current ? 

How far to the north-east do the waters of the Gulf Stream extend ? 

What distant shores are warmed by the waters of the Gulf Stream? By those 
of the Japan Current? 

Why do not the heated waters of the Gulf Stream exert a more powerful 
influence on the climate of the eastern sea-board of the United States? 

Point out the principal cold currents; the principal warm currents? 

Which currents would aid, and which would retard, the progress of a vessel 
in sailing from New York to San Francisco ? From America to Europe ? From 
America to India or Australia ? 



PART IV. 
THE ATMOSPHERE. 

Definition and Function.— The atmosphere, or gaseous por- 
tion of the earth, forms a complete spheroidal shell which sur- 
rounds the solid and liquid globe, and not only rests upon the 
surface of land and sea, but also penetrates them to a great depth. 
It is difficult to imagine life on the earth without the atmosphere. 
By means of the atmosphere the sun's light is diffused over the 
earth, sound is conducted, and birds are enabled to fly. Its 
pressure in all directions reduces the weight of bodies immersed in 
it. It plays an important part in the economy of the earth by re- 
taining and modifying the solar heat, absorbing and distributing 
moisture, supplying animals with oxygen and plants with carbon 
dioxide. When in violent movement, it destroys property and life. 
In its three general movements, waves, tides, and currents, it pro- 
duces water waves and ocean currents, moves ships, drives wind- 
mills, and transports light objects. 

The gases composing it are not united or combined in any way, 
but are almost entirely independent of one another. By the process 
of respiration, oxygen supports the life of all animals and plants, 
and it is the universal agent of combustion. Rusting is the result 
of its union with metals. The chief function of nitrogen is to dilute 
the oxygen. It is of great importance to plant and animal life. A 
few plants, such as clover, alfalfa, peas, and beans, add nitrogen 
to the soil and thus enrich it. The dust particles found in the at- 
mosphere serve as centres about which the water vapor condenses. 
Dust-polluted air is believed to promote decomposition and to 
favor diseases of the lungs, like tuberculosis. 

186 



GENERAL PROPERTIES OF THE ATMOSPHERE. 187 

SECTION I. 
THE ATMOSPHERE, 

CHAPTER I. 
General Properties of the Atmosphere. 

266. Composition. — The atmosphere is a mechanical mixture 
of nitrogen and oxygen, in the proportion, by weight, of nearly 77 
per cent, of nitrogen and 23 per cent, of oxygen. Small quantities 
of two additional elementary constituents of the atmosphere, named 
argon and krypton, have also been discovered. They are inert, like 
nitrogen, and are included with the 77 per cent, of nitrogen above 
referred to. To these must be added a nearly constant quantity of 
carhoniG acid, about 5 or 6 parts in every 10,000 parts of air, or 
about a cubic inch of carbonic acid to every cubic foot of air, and 
a very variable proportion of water vapor. The gaseous ingredients, 
though of different densities, owing to a property of gases called 
diffusion, are found in the same relative proportions at all heights. 

The water vapor is necessary to the existence of plant and animal 
life, especially to the former. It is the water vapor in the air that, 
when condensed, forms clouds, rain, snow, dew, etc. Some little 
water vapor is always present in the air even over the desert parts 
of the earth. 

The water vapor is not, however, equally distributed vertically 
through the air ; a much larger proportion is found in the lower 
than in the upper regions. 

The oxygen and carbonic aoid are the most important of the gaseous constitu- 
ents. Oxygen supports combustion and respiration, and is thus necessary to the 
existence of animal life. Carbonic acid, composed of carbon and oxygen, is the 
source from which vegetation derives its woody fibre, and is thus necessary to the 



188 



PHYSICAL GEOGRAPHY. 



existence of plant life. In respiration, animals take in oxygen and give out car- 
bonic acid ; in sunlight, plants take in carbonic acid and give out oxygen. In 
this way the relative proportions of the substances necessary to the existence of ani- 
mal and plant life are kept nearly constant. 

267. Dust. — Besides the gases and vapor of water in the atmos- 
phere, there are generally present various kinds of mineral dust that 
have been thrown into the air by different causes. The finer parti- 
cles of this dust are carried by the winds to great distances, and 
remain suspended in the air for long periods of time. The dust in 
the air is of importance in determining the temperature, in scatter- 
ing or diffusing sunlight, and, possibly, in aiding or determining the 
formation of fog and clouds under certain circumstances. 

268. Elasticity. — The atmosphere is eminently elastic ; that is, 
when compressed or forced to occupy a smaller volume, it will regain 
its original volume on the removal of the pressure. Air expands 
when heated and contracts when cooled. 

269. Pressure, — So evenly does the atmosphere press on all sides 
of objects that it was a long time before it was discovered that air 

possesses weight. The discovery was made by 
Torricelli, an Italian philosopher and pupil of 
the famous Galileo. The instrument Torri- 
celli employed is called a Barometer. 

270. The Barometer.— The principle of the ba- 
rometer is as follows : A glass tube, about 33 inches in 
length, is closed at one end, filled with pure mercury, 
and carefully heated so as to drive out all the air. 
Placing a finger over the open end, the tube is reversed 
and dipped below the surface of mercury in a cup or 
other vessel. On removing the finger, a column of 
mercury remains .in the tube, being sustained there by 
the pressure of the atmosphere, as shown in Fig. 87. 
Near the sea-level this column is ordinarily about 30 
inches high ; on mountains it is much lower ; in all 
cases the weight of the mercurial column being equal 
to that of an equally thick column of air, extending from the level of the reser- 
voir to the top of the atmosphere. 

Mercurial barometers are made in various forms. In some forms the glass 
tube is encased in a metallic tube, furnished with two slits on opposite sides in 
order to expose to view the mercury column. The divisions are marked on the 




Fig. 87. — Barometer. 



GENERAL PROPERTIES OF THE ATMOSPHERE. 189 




metal tube. A sliding scale, called a vernier, is provided to enable small scale 
divisions to be easily read. Both of these features are shown in Fig. 88. 

When variations occur in the pressure of the atmos- 
phere, corresponding variations occur in the height of the 
mercury in the barometer, the column rising with in- 
creased, and falling with diminished, pressure. 

The entire atmosphere presses on the earth 
with the same weight as would a layer of mer- 
cury about 30 inches in depth. A column of 
mercury 30 inches high, and one square inch in 
area of cross-section, weighs about 15 pounds. 
Therefore, the pressure which the atmosphere 
exerts on the earth's surface, at the level of the 
sea, is equal to about 15 pounds for every square 
inch of surface. The entire weight of the atmos- 
phere, in pounds, is equal to 15 times the number 
of square inches in the earth's surface. 

271. Aneroid Barometer. — Sometimes a hol- 
low, exhausted vessel or cell is employed in place 
of a mercury column ; the barometer is then called 

an aneroid barometer ; 
i. e., a barometer devoid of a liquid. This 
barometer depends for its operation on the 
pressure exerted by the air against a hol- 
low metallic box, partially exhausted of air, 
an increase in pressure causing the top and 
bottom of the box to move toward each 
other, while, on a decrease of pressure, the 
elasticity of the metal causes the top and 
bottom to move away from each other. 
These movements, multiplied by means 
of a suitable arrangement of levers, com- 
municate their movement to a needle which 

moves over a graduated dial. A form of aneroid barometer is shown 

in Fig. 89. 

272. The Barograph, or Self-recording Barometer. — In order 



Fig. 88. — Upper 
Portion of Ba- 
rometer. 




Fig. 89. — Aneroid 
Barometer. 



190 



PHYSICAL GEOGRAPHY. 




Fig. 90.— Ricliard's Barograph. 



to obtain a continuous record of atmospheric pressures some form of 
self-recording barometer is employed ; such an instrument is called 
a barograph. In Eichard's barograph (Fig. 90), as employed by 

the United States 
Weather Bureau, in- 
stead of using a mer- 
cury column to bal- 
ance the varying 
atmospheric pressure, 
an exhausted vessel 
or system of corru- 
gated aneroid cells 
is used. An increase 
of pressure causes the top of the vessel to move toward the bottom. 
On a decrease of pressure, a spring, placed inside the vessel, pro- 
duces a movement in the opposite direction. These movements, 
magnified by a system of levers, cause a pen to trace the successive 
positions on a sheet of paper placed on a recording cylinder, which 
is driven by clockwork in the usual manner. 

273. Isobars ; Isobaric Charts. — Isobars are lines connecting 
places that have the same mean barometric pressure. Isobaric 
charts are charts on which isobaric Hues are drawn. 

In order to be able to compare barometric observations made at 
different elevations, they are reduced to the level of the sea by adding 
to the observed pressure an additional pressure whose value is equal 
to that of the column of air reaching from the place downward to 
the level of the sea. 

In the isobaric chart shown in Fig. 91, it will be seen that the 
barometric pressure varies from about 29.8 inches at the equator to 
about 30.2 inches at 35° N. and 30° S. Lat. respectively. From these 
points the pressure decreases toward the poles. Exact knowledge 
as to actual pressure in the nearer neighborhood of the poles is yet 
wanting. 

274. Height of the Atmosphere. — If the air were everywhere 
of the same density, its height could be easily calculated; but the 



GENERAL PROPERTIES OF THE ATMOSPHERE. 191 







192 



PHYSICAL OEOGRAPHY. 



lower layers are denser than the others, because they have to bear 
the weight of those above them. The density must, therefore, 
rapidly diminish as we ascend. 

By carefully observing the decrease in pressure with the elevation, at differ- 
ent altitudes, and making proper corrections, the heights of mountains may be 
readily determined by the barometer. The measurement of heights by the 
barometer, or similar means, is called Hypsometry. 

If by pressure on a gas we diminish its volume one-half, its density will be 
doubled ; conversely, if the density be diminished one-half, the volume will be 
doubled. The following table, calculated from the law of increase in volume 
with diminished pressure, gives the barometric height, the volume, and the 
density of the air at different elevations above the sea. The elevation of 3.4 
miles is the result of observation ; the other distances are estimated : 



Barometric height 


Volume of given 


Density. 


Estimated distance 


in inches. 


weight of air. 


above sea, in miles. 


30.00 


1 


1 


0.0 


15.00 


2 


i 


3.4 


7.50 


4 


1 


6.8 


3.75 


8 


i 


10.2 


1.87 


16 


tV 


13.6 


.93 


32 


^ 


17.0 



It appears from the above table that by far the greater part of the 
air, by weight, lies within a few miles of the surface, nearly three- 
fourths being below the level of the summits of the highest moun- 
tain-ranges. 

The height of the upper limit of the atmosphere has been vari- 
ously estimated. Calculations based upon the diminution of pressure 
with the height place it at from 45 to 50 miles above the level of 
the sea ; others, based on the duration of twilight, place it at dis- 
tances varying from 35 to 200 miles. 

Above five or six miles the air is so rare that human beings experience great 
difficulty in breathing, as has been the case with those who have ascended lofty 
mountains or made ascents in balloons. 

The form of the atmosphere is that of an oblate spheroid, the 
oblateness of which is greater than that of the earth. 



GENERAL PROPERTIES OF THE ATMOSPHERE. 192a 




192b CLIMATE. 



CHAPTER II. 
Climate. 

275. The Climate of a country is the condition of its atmosphere 
as regards heat or cold, moisture or dryness, and healthiness or 
unhealthiness. It also embraces the average succession of weather 
changes throughout the year. 

276. Temperature. — The temperature of the atmosphere is deter- 
mined by means of an instrument called a thermometer. 

The thermometer consists of a glass tube of very fine bore, furnished at one 
end with a bulb. The tube is carefully dried, and the bulb filled with pure mer- 
cury and heated in the flame of a spirit-lamp ; the mercury expands, and, filling 
the tube, a portion runs out from the open end, thus efi'ectually expelling the air. 
A blowpipe flame is then directed against the open end, and the tube is fused, 
, and thus hermetically sealed. As the bulb cools, the mercury contracts, and 
leaves a vacuum in the upper part of the tube. The instrument will now indi- 
cate changes in temperature ; for, whenever the bulb grows warmer, the column 
of mercury expands and rises; when it grows colder, it contracts and falls. 

In order to compare these changes of level they are referred to certain fixed 
or standard points: the freezing- and boiling-points of pure water. These are 
obtained by marking the respective heights to which the mercury rises when 
the thermometer is plunged respectively into melting ice and into the steam 
escaping from boiling water. In Fahrenheit's scale the freezing-point is placed 
at 32°, the boiling-point at 212°, and the space between these two points is 
divided into 180 (212 — 32) equal parts, called degrees. In the Centigrade scale 
the freezing- and boiling-points are respectively 0° and 100°. Fahrenheit's 
degrees are represented by Fahr. or F., thus, 212° Fahr. or 212° F. ; Centigrade's 
by Cent, or C, as 100° Cent, or 100° C. 

Since mercury freezes at —39° C, temperatures lower than this are very 
often measured by means of alcohol thermometers, for the freezing point of alco- 
hol is —130° C. Shnilarly, since the boiling point of mercury is 360° C, mer- 
cury thermometers cannot be used for measuring very high temperatures. A 
gas thermometer is the standard instrument for all temperatures. 

The fact that metals have different rates of expansion gives us the metallic 
thermometer. A compound metallic ribbon is wound in helical form. End a is 
fixed, while the other end is attached to a lever arm b, the motion of which 



CLIMATE. 



193 





Fig. 91a.— A Metallic 
Thermometer. 



in water. This form of tlier- 
moraeter is designed to meas- 
ure the quantity of moisture 
in tlie atmosphere, and is 
called a hyqrometer (see page 
222). 

277- Temperature and 
Heat. — Heat is the result of 
a certain kind of insensible 
motion of the molecules of 
matter. Temperature is used 
to denote the condition or 
degree of hotness or coldness 
of the body whose state is 
being described. From a 
sufficient number of temper- 
ature records, spread prop- 
erly over a year, an average 
temperature for that year 
may be obtained. Similarly, 
averages for shorter periods, 
as seasons, months, and days, 
are possible, called average 
seasonal, monthly, and daily 
temperatures. The average 
temperature of one year for 
a given place is, as a rule, 
somewhat different from that 
13 



rotates the pointer d over 
the dial. The more expan- 
sible metal is on the outside. 
Else in temperature causes 
the helix to wind up closer, 
the index moving to the 
right; a decrease causes it 
to unwind, the point moving 
to the left. 

The wet and dry bulb ther- 
mometer (see figure) consists 
of two ordinary thermome- 
ters, the bulb of one of 
which is covered by a small 
piece of cloth kept constantly 
moist by a wick immersed 




Fig. 91b.— A Fahrenheit Thermometer. A Hy- 
grometer with Wet and Dry Bulbs. 



194 



PHYSICAL GEOGRAPHY. 



of the preceding or following year. The average temperature for a goodly num- 
ber of years gives its viean annual temperature. In the same way it is necessary 
to take the averages for many Julys to get the mean monthly temperature. 

In general, we can count on a decrease of about 1° F. for an increase of one 
degree in latitude, and we can associate areas of low barometric pressure with* 
high temperatures and areas of high pressure with low temperatures. 

278. The Thermograpli or Self-recording Thermometer. — 
When it is desired to make a continuous record of the variations 
in temperature at any place, some form of self-recording thermometer 
or thermograph is employed. Richard's thermograph, the form 

employed in the United 
States Weather Bureau. 
is shown in Fig. 92. 
The thermometer con- 
sists of a metallic tube, 
T, elliptical in cross- 
section, and curved as 
shown in the figure. One 
end of the tube is firmly 
fixed to a support, s, con- 
nected with the frame 
of the apparatus, and the other end left free to transmit its move- 
ments to a system of levers. The tube is filled, under pressure, with 
alcohol or similar liquid having a low freezing-point. Changes of 
temperature produce corresponding changes in the curvature of the 
tube, these movements being communicated by the system of levers 
as shown, and recorded on the record paper placed on the recording 
cylinder. The record cylinder is driven by clock-work in the usual 
manner. 

279. Causes of the Greater Heating Power of the Vertical 
Rays of the Sun than of the Oblique Rays. (Fig. 93.) 

(1) The Vertical Rays are Spread Over a Smaller Area. — Equal areas 
of the sun's surface give off equal quantities of heat. If, therefore, 
the sun's rays between a and b, and between c and d, come from 
equal areas, the amounts of heat they carry will be equal; 




Fig. 92.— Richard's Thermograpli. 



CLIMATE. 195 

while the heat given off from a b, the more nearly vertical rays, is 
spread over the earth's surface from / to g, that from c d, the more 
oblique rays, is spread over the greater area hi; the area / g, 
therefore, which receives the more nearly vertical rays, is much 
warmer than h i, where the obliquity is greater. 

(2) The Yertical Rays Pass Through a Thinner Layer of Air. — Only 
a part of the sun's heat reaches the surface of the earth ; about 28 
per cent, of the vertical rays are absorbed during their passage 
through the atmosphere. The amount of this absorption must 
increase as the length of path increases. In the figure, the light 
shading represents the atmosphere. It is clear that the oblique 
d c b a 

1 f I : : I 

I 



! i ! I : ^ 

: I I , , 



Fig. 93.— Causes of the Greater Healing Power of the Vertical than of the 

Oblique Rays. 

rays pass through a thicker stratum of air than the more direct 

ones, and, therefore, are deprived of a greater amount of heat. 

According to Laplace, the thickness of the stratum of air traversed by the 
rays when the sun is at the horizon is 35.5 times greater than when it is directly 
Overhead. A similar absorption of light similarly influences the comparative 
brightness of sunlight in diflferent latitudes. 

(3) The Vertical Rays Strike More Directly, and, therefore, Produce 
More Heat. — The heating power of the more nearly vertical rays is 
greater than that of the rays which strike obliquely. 

280. Variations in Temperature. — The differences in the heat- 
ing power of the vertical and oblique rays of the sun cause the tem- 
perature of the earth's surface to decrease gradually from the equator 
toward the poles. The differences of temperature thus effected are 
further increased by the difference in the length of daylight and 



196 PHYSICAL GEOGRAPHY. 

darkness. While the sun is shining on any part of the earth the air 
is gaining as well as losing heat ; while it is not shining, the air is 
only losing heat. When the length of daylight exceeds that of the 
darkness, the gain usually exceeds the loss ; when the darkness 
exceeds the daylight, the loss exceeds the gain. 

The excessively low temperature that would result from the oblique 
rays in high latitudes is prevented by the great length of daylight 
during the short summers, thus allowing the sun to continue heating 
the surface during longer periods. The warmest part of the day in 
high latitudes sometimes equals that in the equatorial regions. Dur- 
ing the long winters, however, the continued loss of heat makes the 
cold intense. 

Hence in the tropics we find a continual summer; in the temperate 
zones, a summer and a winter of nearly equal length ; and in the polar 
zones, short, hot summers, folloived by long, intensely cold winters. 

281. Manner in -which the Atmosphere receives its Heat 
from the Sun. — The atmosphere receives its heat from the sun — 

(1) Directly. — As the sun's rays pass through the air, about 28 
per cent, of the heat is directly absorbed, thus heating the air. The 
remainder passes on and either heats the earth or is reflected from 
its surface. 

(2) From the Seated Earth. — The sun's rays heat the earth and the 
heated earth heats the air. It does this in three ways : 

(a) By the air coming in contact with the heated earth. As the 
layer of air in contact with the ground becomes heated, it expands 
or grows lighter, and is displaced by cooler and heavier air, which, in 
its turn, is heated and displaced, layer after layer being thus 
brought into contact with the heated earth. - 

(6) By the heated earth radiating its heat, or sending it out 
through the air in all directions. 

After the sun's heat has been absorbed by the earth and radiated 
from it, a change occurs which renders the rays much more readily 
absorbed by the air. 

(c) By the heat being reflected from the earth and again sent 
through the air. But little heat is imparted to the air in this way. 



CLIMATE. 197 

Clear, dry air absorbs but little of tbe sun's heat. It is mainly 
the dust particles that absorb the heat of the sun's rays and so heat 
the air around them. Since the lower layers of the air contain a 
greater proportion of dust particles, the upper layers containing com- 
paratively little dust, the lower layers heat readily by day, while the 
upper layers are nearly unaffected. But the dust particles are good 
radiators of heat ; that is, they throw it off readily in all directions. 
Hence, during night, they rapidly lose their heat, and cool the sur- 
rounding air. Consequently, the upper layers of the atmosphere pos- 
sess a nearly uniform temperature, while the lower layers are charac- 
terized by marked changes in temperature ; i. e., warm during the 
daytime and cold at night. It was formerly believed that it was 
the aqueous vapor in the air that absorbed most of the sun's heat, 
but it has been shown, by more careful experiments, that it is not 
the true water vapor but the minute particles of water suspended in 
the air that have the same power as dust particles in absorbing and 
radiating heat. 

282. Isothermal Lines are lines connecting places on the earth 
which have the same mean temperature. 

The Mean Daily Temperature of a place is obtained by taking the 
average of its temperatures during twenty-four consecutive hours. 

The Mean Annual Temperature of a place is the average of its 
mean daily temperatures throughout the year. 

Maps showing the distribution of temperature are called thermal 
maps. An isotherm connecting places having the same mean annual 
temperature is an annual isotlierm. The charts on page 197 show 
that the annual temperature is highest near the equator, and that it 
becomes lower toward the poles. This shows the relation between 
temperature and latitude (page 194). These charts show the iso- 
therms for the months of January and July. Note how the lines 
shift with the sun. Thus, the July isotherm of 50° in the northern 
hemisphere is about where the isotherm of 20° was in January. 
Notice, also, that the difference in temperature between January 
and July is much greater in high latitudes than in low. Thus, in 
the southern part of Hudson Bay there is 70° difference between 



197c PHYSICAL GEOGRAPHY. 

January and July ; at Lake Erie, about 45° ; in Florida, about 20° ; 
and at the ecjuator in South America, less than 10°. The same 
charts show that the difference is greater in the interiors of conti- 
nents than on coasts or over the sea in the same latitude. Thus, in 
the interior of North America, west of Hudson Bay, the difference 
is about 80°, while on the coast of Alaska it is only about 30°. 

Courses of the Isothermal Lines.— 1. The courses of the iso- 
therms are roughly parallel to the parallels of latitude. Since the 
isotherms do not follow the parallels exactly, it is clear that some 
other cause besides the length of day and the angle of the sun's 
rays must influence tempei'ature. 

2. The maps show that the isotherms are straightest where there 
is little laud, and most crooked where there is much land. This 
suggests that land and tvater have something to do with their posi- 
tions. The irregularities of the isotherms of the northern hemi- 
sphere in July are much greater than those of the southern hemi- 
sphere in January (summer in the southern hemisphere). This is 
probably on account of the greater land area in the northern hemi- 
sphere. 

3. The bends of the isotherms are not as pronounced on the east 
sides of the continents as on the west. This is not explained by 
latitude, or by the distribution of land and ocean. Such peculiarities 
may be explained by the winds. The prevailing winds in the 
middle latitudes of North America are from the west, and tend to 
carry the warmer temperature of the sea (in winter) over the land on 
the western side, and the cooler temperature of the land (in winter) 
over the sea, on the eastern side of the continent. 

4. Citrrents in the ocean affect isotherms. This explains the 
great bend in the 30° isotherm in the North Atlantic in January. 

5. There are other causes of irregularities in the isotherms, A 
basin region, shut in by mountains, gets hotter in summer than 
an open region. A dry surface, through absence of evaporation, 
will be warmer than a moist one. Color of the soil, presence or 
absence of vegetation, also affect the absorption and radiation of 
heat. 



CLIMATE. 197d 

The high temperature (90° and higher) in the southwestern part 
of the United States in July is accounted for partly by the fact 
that the region is somewhat shut in by mountains. The dryness 
of the soil and of the air above it also tends to raise its temperature. 
Aridity also helps to make the temperature high in Northern Africa 
in July, and in Australia in January. 

Altitude affects temperature, but isothermal charts show no rela- 
tion between isothermal lines and surface relief. The reason is 
that isothermal lines are represented on maps as if they were at sea 
level. This is done by making allowance for altitude at the aver- 
age rate of 1° F. for about 330 feet. Thus if the. temperature of a 
place at an altitude of 3,300 feet is 60°, it is put down on the 
charts as 70° (60° + 10°). If the place were 6,600 feet above sea 
level, 20° F. would be added to the temperature recorded by the 
thermometer. 

The Cold Pole and the Polar Caps. — The cold poles are the 
points supposed to be the coldest in the northern hemisphere. One 
is near Verkhoyansk, Siberia, where the temperature drops to 
-90° F. Another very cold region is near Van Rensselaer Har- 
bor, North America. The isotherm of 50° for the warmest month 
in each hemisphere is about the polar limit for cereal grains and 
forest trees. These lines surround two caps of polar climate be- 
tween which lies the whole habitable world. 

In considering temperature, if the station remains constant while 
the readings are taken at different times, a temperature curve is 
produced. If the readings are all taken at the same time but at 
different places, an isothermal line is produced. 

The Temperature Gradient. — The vertical temperature gradient 
is the change of temperature of the air per unit of altitude, usually 
expressed in degrees C. per 100 metres. By international agree- 
ment it is defined as positive when the temperature decreases with 
increasing altitude. 

283. Climatic Belts. — The Physical Torrid Zone lies on 
both sides of the equator, between the annual isotherms of 70° 
Fahr. 



198 PHYSICAL GEOGRAPHY. 

The Physical Temperate Zones lie north and south of the Physical 
Torrid Zone, between the annual isotherms of 70° and 30° Fahr, 

The Physical Frigid Zones lie north and south of the Physical 
Temperate Zones, from the annual isotherms of 30° Fahr. to the 
poles. 

The greatest mean annual temperature in the Eastern Hemisphere 
is found in portions of North Central Africa, in Arabia near the 
Red Sea, in the southern part of Hindostan, and in the northern 
part of New Guinea and the neighboring islands ; in the ^V^estern 
Hemisphere, it is found in the northern parts of South America 
and in Central America. 

The Heat Equator, or the isotherm of greatest mean annual tem- 
perature, does not coincide with the Geographical Equator, but lies 
generally to the north of it. 

284. Modifiers of Climate. — The principal modifiers of climate ; 
i. e., the causes which prevent the isothermal lines from coinciding 
with the parallels of latitude, are : 

(1) The Distribution of the Land- and "Water-areas. — Land 
both heats and cools rapidly. Land is a good absorber of heat, and 
heats readily during the day, but this heat is limited to a com- 
paratively thin layer, and, since the capacity of land for heat is 
small, the heat absorbed produces a great rise of temperature. 
Land is a good radiator, and, therefore, readily loses heat; and, 
since this loss is from a comparatively thin layer only, cools rapidly 
at night. 

Therefore, a comparatively short exposure of land to heating 
produces a high temperature, and a comparatively short exposure 
to cooling produces a low temperature. 

Water, on the contrary, both heats and cools slowly, absorbing or 
emitting large quantities of heat. This is because water has a great 
capacity for heat. The heat penetrates a comparatively deep layer, 
and as soon as slightly heated, the warmed water is replaced by cooler 
water. Moreover, a considerable proportion of the sun's rays is 
directly reflected from the surface of the water, and thus passed 
back again through the air. Nor can the ocean water readily lose 



CLIMATE. 199 

its heat and become cold, since water is a poor radiator, and when 
the surface layers are cooled they sink, and are replaced by warm 
water from below. 

Therefore, the water may be exposed to either long heating or 
long cooling without growing very hot or very cold. The tempera- 
ture of the ocean seldom varies more than 3° Fahr. during the day, 
or more than 15° Fahr. during the year. 

Consequently, the land is subject to great and sudden changes of tem- 
perature ; the water, to small and gradual changes. 

Places situated near the sea have, therefore, a more equable, uni- 
form climate than those in the same latitude in the interior of the 
continent. The former are said to have an oceanic climate; the 
latter, a continental climate. 

In the polar regions, a preponderance of moderately elevated land- 
areas causes a colder climate than an equal area of water, because 
land loses heat more rapidly than water. 

In the tropics, a preponderance of land-areas causes a warmer cli- 
mate than an equal area of water, because land gains heat more 
rapidly than water. 

(2) Elevation. — The temperature of the atmosphere rapidly de- 
creases with the elevation. The decrease is about S** Fahr. for 
every 1000 feet. 

The lower layers of the air are warmer than the upper layers 
because : 

(a) They are nearer the heated earth. 

(6) They contain more dust and water particles, and, therefore, 
can more readily absorb and stop the sun's heat while it is passing 
through them. 

(c) They are more directly heated by the secondary radiation 
from the heated earth. 

(d) They are heated by the condensation of the upper air as it 
falls to the earth's surface. 

The effect of elevation is so powerful that on the sides of high tropical moun- 
tains similar changes occur in the vegetation as are ohserved in passing from the 
equator to the poles. 



200 PHYSICAL GEOGRAPHY. 

(3) Direction of the Slopes. — That slope of an elevation on 
which the sun's rays fall in a direction most nearly at right angles 
to its surface will be the warmest. 

In the Northern Hemisphere the southern slope of a hill is warmer in winter 
than the northern slope, because the rays fall more nearly at right angles to its 
surface. 

(4) Position of the Mountain-ranges. — A mountain-range will 
make the country near it warmer if the wind from which it shields 
it is cold ; it will make it colder, if such wind is warm. 

The position of the mountain-ranges of a country also greatly affects the dis- 
tribution of its rainfall. Thus, the tropical Andes are well watered and fertile 
on their eastern slopes, but dry and barren on their western. The prevailing 
moist trade- winds, forced to ascend the slopes, deposit all their moisture on them 
in abundant showers, and are dry and vaporless when they reach the other side. 
Valleys are not subject to as great extremes of temperature as are hill-tops or 
mountains, since the hill-sides do not permit free radiation. 

(5) Nature of the Surface. — The temperature of a tract of 
land is greatly affected by the nature of its surface. If covered 
with abundant vegetation, like a forest, or if wet and marshy, its 
surface heats and cools slowly, and has a comparatively uniform 
temperature ; but if destitute of vegetation, and dry, sandy, or rocky, 
it both heats and cools rapidly, and is subject to great extremes of 
temperature. 

(6) Distribution of "W"inds and Moistiire. — The principal 
action of the winds, and their accompanying moisture, is to mod- 
erate the extremes of temperature by the constant interchange 
between the heat of the equatorial and the cold of the polar regions. 
Both wind and vapor absorb and render latent large quantities of 
heat in the equatorial regions, and give it out, in higher latitudes, 
bn cooling. In cold countries the climate is rendered considerably 
warmer by the immense quantity of heat thus emitted by the con- 
densed vapor. 

(7) Ocean Currents. — Since the warm waters move to the polar 
regions, and the cold waters to the equatorial regions, the general 
effect of ocean currents on climate is to reduce the extremes of 
temperature. 



THE WINDS. 



201 



The combined effects of the action of the winds, moisture, and 
ocean currents are seen in the northern continents, whose western 
shores, under the influence of the prevailing south-westerly winds, 
copious rains, and tropical currents, are considerably warmer than 
the eastern shores in the same latitude. 

The coasts of Great Britain are warm and fertile, wMle Labrador, in the same 
latitude, is cold and sterile. The island of Sitka, in the Pacific, is warmer than 
Kamtchatka, firom similar causes. 



►o>*4c 



CHAPTER III. 

The Winds. 

285. Winds are masses of air in motion. In general, they 
resemble ocean currents, and are due to the same causes ; viz., dif- 
ferences of density caused by differences of temperature. 

286. Barometric Gradient ; Origin of Winds ; Convection. 
— When any part of the earth's surface becomes heated more than 
neighboring parts, 

such as the heated 
area, a a, in Fig. 94, 
the air over that part, 
becoming heated, ex- 
pands, and, growing 
lighter, rises, pushing 
away the air over it 
toward the colder re- 
gions shown on the 
right and left. As it 
rises it expands, and 

thus becomes cooled. At the same time the colder, denser air from 
over the less heated areas on the sides flows in as surface currents 
toward the heated area, at the same time receiving the upper cur- 
rents from over the heated area, which, as they fall, are compressed, 
and thus raised in temperature. 



A / 


, 


b 


6 


1 1 


1 1 




^J 



Fig. 94.— Origin of Winds. 



202 PHYSICAL GEOGRAPHY. 

There thus results a decrease in the barometric pressure over the 
heated area, and an increase in the barometric pressure over the 
cooler areas. The differences in temperature also cause a movement 
of the warmed air toward the cooler regions, and a movement of 
the cooled air toward the warmer regions. This process is called 
convection. 

Generally speaking, differences in temperature result in differ- 
ences of barometric pressure, the pressure over heated areas being 
generally less than the pressure over cool areas. Differences in 
pressure establish a slope, or gradual variation in pressure, called 
the barometric gradient. The air moves as a surface wind or cur- 
rent from a higher to a lower barometric pressure, or from a colder 
to a warmer area, as shown in Fig. 94. An examination of this 
figure will show that the differences of temperature have produced 
the following currents or winds : 

(1) Ascending currents, h b, over the heated area ; 

(2) Lateral inflowing surface currents, c c, from the adjoining 
cooler areas ; 

(3) Lateral outflowing upper currents, d d, from the heated areas ; 

(4) Descending currents, e e, over the cooler areas. 

These movements depend solely on differences of temperature. 
They continue as long as differences of temperature continue, and 
cease as soon as they cease. 

287. Origin of the Atmospheric Circulation. — Generally 
speaking, the temperature of the earth's surface gradually decreases 
from the equator toward the poles. The hottest portions of the 
earth's surface are situated within the tropics, and the coldest por- 
tions are near the poles. Consequently, we should expect to find 
an area of lowest barometric pressure in the equatorial regions, and 
an area of high barometric pressure near the poles; or, in other 
words, the barometric gradient should slope from the poles toward 
the equator. In point of fact, we do find the cooler air from 
the polar regions blowing as surface currents toward the heated equa- 
torial regions, and as ascending currents near the equator, which, 
after reaching a certain elevation, blow as upper currents toward 




130 Longitude 140 East from ICO Qreenwich ISO 




Longimde 40 "West from 20 Greenwich Longitude 20 East from 40 Greenwich 



100 120 



TSE WINDS. 203 

the poles. Currents thus result, by means of which the entire mass 
of the atmosphere is kept in constant circulation, and an interchange 
effected between the air at the equator and that at the poles. 
The most important of these currents are the following : 

(1) Polar currents, blowing along the earth's surface from the 
poles to the equator. 

(2) Equatorial currents, or upper currents, which blow from the 

equator toward the poles. 

In speaking of winds, reference is always made to surface currents, unless 
otherwise stated. 

It will be noticed that wherever the surface wind blows in any- 
given direction, the upper wind blows in the opposite direction. 

In several instances the ashes of volcanoes have been carried great distances 
in directions opposite to that in which the surface wind was blowing. The smoke 
from tall chimneys at first takes the direction of the surface wind, but rising, is 
soon carried in the opposite direction by the upper currents. The clouds are 
often seen moving in a direction opposite to that indicated by vanes placed on 
the tops of the houses. 

A current of air is named according to the direction from wfiich it 
comes; a current of water, according to the direction in which it is 
going. Thus, a north-east wind comes from the north-east ; a north- 
east current of water goes toward the north-east. 

288. Actual Barometric Gradient. — The barometric gra- 
dient is by no means so simple as we might imagine. A number 
of causes prevent the simple distribution of atmospheric pressure, 
and the movement of the equatorial and polar currents. In 
the first place, the fall of temperature is by no means uniform 
from the equator to the poles ; nor does the Seat Equator coincide 
with the Geographic Equator. Moreover, the rotation of the earth 
tends to deflect the equatorial and polar currents from their merid- 
ional, or true north and south paths, thus bringing about a dis- 
tribution of the air which greatly modifies the barometric gradient 
as established by mere differences of temperature. 

The modifications produced by these and possibly other causes 
may be seen by a study of the isobaric chart shown in Fig. 91, in 
which it will be seen that an irregular belt or zone of fairly low 



,204 PHYSICAL GEOGRAPHY. 

pressure surrounds the earth near the equator, and that the pressure 
generally increases up to about 35° to 40° N. Lat. and 30° to 35° 
S. Lat., as shown by the irregular belts which have their central 
portions in these latitudes. From these regions of high pressure 
the pressure decreases toward the poles, the decrease being most 
marked in the Southern Hemisphere. A tendency exists for the 
wind to rotate about these centres of pressure. A great circum- 
polar whirl is believed to be produced in the polar wind as it 
moves toward the equator, and this, most probably, is the cause 
of the area of low pressure at the poles. 

289. Efifect of the Earth's Rotation in the Direction of the 
Wind; Perrel's Law. — Were the earih at rest, the polar and 
equatorial currents would blow due north and south along the 
meridians, but on account of the rotation from west to east, a tend- 
ency exists to deflect all horizontal currents, in whatever direc- 
tion they may be moving, to the right in tlie Northern Hemi- 
sphere, and to the left in the Southern Hemisphere. The greater 
the velocity with which the current is moving, the greater will be 
the amount of the deflection. The deflection is greater also in high 
latitudes than near the equator. As thus deflected by the earth's 
rotation, the polar currents blow from the north-east in the North- 
ern Hemisphere, and from the south-east in the Southern Hemi- 
sphere ; the equatorial currents blow from the south-west in the 
Northern Hemisphere, and from the north-west in the Southern 
Hemisphere. 

290. Interchange of Surface and Upper Currents.— The 
equatorial currents do not continue as upper currents all the way 
to the poles, but fall, and become surface currents, replacing the 
polar winds, which rise and continue for a while toward the equator 
as upper currents. This interchange is due to a variety of causes, 
the principal of which are the decreasing areas of the earth's zones 
as indicated by the converging of the meridians and the gradual 
chilling of the equatorial upper currents. 

291. Classification of Winds. — Winds are divided into three 
•classes : 



THE WINDS. 205 

(1) Terrestrial^ the planetary or prevailing winds whose direction remains 
the same throughout the year. 

(2) Continental^ or those which for regular periods blow alternately in 
opposite directions as monsoons, sea and land, valley and mountain breezes. 

(3) Cyclonic^ or temporary winds or storms blowing in the lower atmos- 
phere towards warmer sections. 

292. "Wind Zones. — The principal wind zones are the Zone of 
Equatorial Calms, the Zones of the Trade-winds, the Zones of the 
Calms of Cancer and Capricorn, the Zones of the Westerly Winds, 
and the Zones of the Polar Winds. All these zones are best 
observed on the ocean. On the land, local differences of tempera- 
ture tend to disturb the boundaries of the zones and the direction 
of the winds. 

293. The Zone of Equatorial Calms, sometimes called the Dol- 
drums, lies near the equator, between the limits of the north-east 
and the south-east trades, over the zone of least barometric pressure. 
Here the ascending currents tend to neutralize the inblowing polar 
currents, thus producing an unstable calm that is liable to be dis- 
turbed at intervals by strong winds. The boundaries of the zone 
vary with the season, moving to the north, during the summer of 
the Northern Hemisphere, and to the south during its winter. The 
sultr}', humid air, with its baffling breezes, too feeble to carry a 
vessel on its course, together with the frequent rains, make this 
region much dreaded by sailing vessels. 

294. The Zones of the Trades are in strong contrast to the 
2one of calms. Here the winds blow with marked regularity from 
the north-east in the Northern Hemisphere, and from the south-east 
in the Southern Hemisphere. It is by reason of this steadiness and 
the aid they afford the intelligent navigator, that they have received 
their name of trade-winds. The trade-winds appear to average two 
miles in depth, since only the higher mountains situated in their 
course rise above them into the oppositely flowing westerly winds, 
or anti-trades. 

295. The Zones of the Calms of Cancer and Capricorn, 
sometimes called the Horse Latitudes, are less distinct zones of 
calms. They are situated between the higher latitude limits of 



206 



PHYSICAL GEOGRAPHY. 



the trades and the zones of the westerly winds. The calms are 
frequently disturbed by light, variable winds. 

296. The Zones of Prevailing "Westerly Winds extend from 
the limits of the Zones of the Calms of Cancer and Capricorn across 
the temperate zones, and at times even into the polar regions. Tneir 
general directions are south-west in the Northern Hemisphere, and 
north-west in the Southern Hemisphere. Storms are common in 
these wind zones. 

297. The Zones of the Polar "Winds extend from the limits 
of the Zones of the Prevailing Westerly Winds to the poles. This 
region is not yet thoroughly explored. There will, probably, be 
found in parts of these zones a region of comparative calms, with 
occasional surface winds from the north-east in the Northern Hemi- 
sphere, and from the south-east in the Southern. 

298. Shifting- of the "Wind Zones. — The entire system of the 
surface winds follows the sun in its movements north or south of the 
equator. For this reason in parts of each hemisphere, between the 
zones of the trades and the zones of the prevailing westerly winds, 
there exist zones called the Sub-tropical Wind Zones, which have 
the trade-winds during the summer in that hemisphere, and the 
westerly winds during its winter. 

299. Dove's Law of Rotational Displacement of the Winds. — The equa- 
torial and polar currents usually displace each other, and become surface winds in 

a regular order, first discov- 
ered by Prof. Dove of Berlin. 
In the Northern Hemi- 
sphere, before the polar cur- 
rent is permanently estab- 
lished from the north-east, 
the wind blows in regular 
order from the west, north- 
west, and north. The dis- 
placement of the polar by 
the equatorial currents oc- 
curs in the opposite direc- 
tion : from the east^ south- 
east, and south, before the general south-west current is permanently established. 
In the Southern Hemisphere these motions are reversed. 



NORTHERN HEMISPHERE. SOUTHERN HEMISPHERK. 




Fig. 95.— Rotational Displacement of Winds. 



THE WINDS. 



207 




Fig. 96. — Land and Sea Breezes. 



This rotational displacement of the winds, together with the effects produced 
on the thermometer and barometer, is indicated in Fig. 95. Since the equatorial 
currents are warm, moistj and light, when they prevail the thermometer rises and 
the barometer falls. On the establishment of the polar currents, however, the 
thermometer falls and the barometer rises. 

300. Land and Sea Breezes. — During the day the land near the 
coast becomes warmer than the sea. An ascending current, there- 
fore, rises over the land, 
and a breeze, called the 
sea breeze, sets in from the 
sea. At night the land-, 
from its more rapid cool- 
ing, soon becomes colder 
than the water ; the as- 
cending current then rises 
from the water, and a 
breeze, called the land 
breeze, sets in from the land. The strength of these winds depends 
upon the difference in tho temperature of the land and water ; they 
are, therefore, best defined in the tropical and extra-tropical regions, 
though they may occur in higher latitudes during the hottest parts 
of the year. Land and sea breezes are periodical winds. 

301. Monsoons are periodical winds which, during part of the 
year, blow with great regularity in one direction, and during the 
remainder of the year blow in the opposite direction. They are 
in reality huge land and sea breezes, caused by the difference in 
temperature between the warmer and colder halves of the year. 
They occur mainly in the regions of the trades, and are in reality 
trade-winds which have been turned out of their course by the 
unequal heating of land and water. 

During winter, in either hemisphere, the oceans, being warmer 
than the land, cause a greater regularity in the trades ; but during 
summer, the tropical continents become intensely heated, and their 
powerful ascending currents cause the equatorial currents to blow 
toward them as surface winds, and thus displace the trades. The 
interval between the two monsoons is generally characterized by 



208 PHYSICAL GEOGRAPHY. 

calms, suddenly followed by furious gales, that may blow from any 
quarter. 

While especially marked in the tropical regions, monsoons also 
occur in the temperate, and even in the polar regions. 

302. Monsoon Regions. — There are three well-defined regions 
of monsoons — the Indian Ocean, the Gulf of Guinea, and the Mexi- 
can Gulf and Caribbean Sea. The first is the largest and most 
distinctly marked. 

Monsoons of the Indian Ocean. — Here the trades are deflected 
by the overheating of the continents of Asia, Africa, and Australia. 

In the Northern Hemisphere the north-east trades prevail with great regularity- 
over the Indian Ocean, during the cooler half of the year (from October to April), 
but during the warmer half (from April to October) the heated Asiatic Continent 
deflects the trades, and the equatorial currents prevail from the south-west. The 
same winds also prevail south of the equator, on the western border of the ocean, 
along the eastern coast of Africa as far south as Madagascar. 

In the Southern Hemisphere, in the south-eastern portion of the Indian Ocean, 
the south-east trade is similarly deflected by the Australian Continent. Here 
the winds blow south-east during the southern winter, and north-west during 
its summer. 

Monsoons of the Gulf of Guinea. — Here the north-east trades 
are deflected during the summer by the intensely heated continent 
of Africa. The south-west monsoon blows over the land as far 
inland as the Kong Mountains. 

Monsoons of the Mexican Gulf and the Caribbean Sea. — In 
this region the north-east trade-winds are deflected during the warmer 
part of the year by the overheating of the Mississippi Valley. 

Besides the preceding well-marked regions, nearly all the coasts of the conti- 
nents in and near the tropics, as the western coasts of Mexico, the eastern and 
western coasts of South America, and the western and northern coasts of Africa, 
have small monsoon regions. 

303. Mountain Winds. — During the day the elevated slopes of 
mountains make the air over them warmer than at corresponding ele- 
vations over the valleys. Currents, therefore, ascend the valleys toward 
the mountains during the day. During the night, however, the air 
near the summits becomes colder than that near the base. Currents, 
therefore, descend the valleys from the mountains during the night. 



STORMS. 



209 



CHAPTER IV. 

Cyclonic Winds and Storms. 

304. Storms are violent disturbances of the ordinary equilibrium 
of the atmosphere by wind, rain, snow, hail, or thunder and light- 
ning. 

During storms the wind varies in velocity from that of a scarcely 
perceptible breeze to upward of 200 miles per hour. 

Velocity and Name of Winds. 



Velocity of Wind in 
Miles per Hour. 


Common Names of Winds. 


1 


Hardly perceptible breeze. 


4 to 5 


Gentle wind. 


10 to 15 


Pleasant brisk gale. 


20 to 25 


Very brisk. 


30 to 35 


High wind. 


40 


Very high. 


50 


Storm. 


60 


Great storm. 


80 


Hurricane. 


100 


Violent hurricane. 


80 to 200 


Tornado. 



305. Tropical Cyclones are storms of considerable extent, often 
covering areas from one to three hundred miles in diameter. They 
consist of vast travelling areas of low barometer with spiral inflow- 
ing currents directed toward a central area of low pressure. They 
are attended by the formation of dense cloud masses, heavy rainfall, 
and vivid lightning discharges with accompanying thunder. At the 
centre, or " eye of the storm," where the pressure is least, there is 
a calm, with clear sky. On the margins of the calm centre, espe- 
cially on the margin toward which the storm is advancing, the pres- 
sure is high. These storms have two distinct motions : a spiral, inflow- 
*.ng, or rotary motion, and a progressive motion, whei-eby the storm 
advances bodily. 

- The general term Cyclones has been applied to these storms on 
14 



210 PHYSICAL GEOGRAPHY. 

account of their rotary motion. They have also various local 
names. 

Cyclones originate in the tropical regions, but frequently extend 
far into the temperate zones. 

306. Regions of Cyclones. — There are five regions of cyclones, 
all of which lie on the western borders of the ocean. These are : 

(1) In the North Atlantic, in the neighborhood of the West Indies. 
Here they are generally called hurricanes. 

(2) In the North Pacific, in the neighborhood of the China Seas, 
where they are generally called typhoons. 

(3) In the South Indian Ocean, east of Madagascar, in the neigh- 
borhood of the Mauritius Islands. 

(4) In the South Pacific, east of Australia. 

(5) In the North Indian Ocean, in the Bay of Bengal. 

In each of these regions the storms occur about the time of the 
change of the regular winds, and have their origin in marked differ- 
ences of temperature; thus in the Indian Ocean and the China Seas, 
they generally occur at the change of the monsoon, after the greater 
heat of summer. 

307. Cause of Cyclones. — Cyclones are convection phenomena ; 
i. e., they originate in an area of low barometer caused by the ascend- 
ing current of air which follows the overheating of any region. As 
the air rushes in from all sides, it is deflected by the earth's rotation, 
and assumes a spiral inflowing or rotary motion around the heated 
area. The centrifugal force generated by this rotation causes the 
barometric pressure of the area to become lower, and the area to 
grow larger. The calm centre is due initially to the heated area 
and the ascending current. After the storm is established and 
moves bodily forward, the calm centre is continued by reason of 
the centrifugal force, which heaps up the air on the sides and 
depresses it in the centre. Meanwhile, the inflowing air, as It 
ascends, is chilled by expansion sufficiently to condense its vapor 
rapidly. The heat energy, previously latent in the vapor, is now 
disengaged, and causes the air to mount higher and condense still 
more of its vapor. It is to the energy thus rapidly liberated by the 



STOBMS. 



211 



condensation of vapor, that the violence of the cyclone is due. 
Cyclones, therefore, acquire extraordinary violence only when an 
abundance of vapor is present in the air. 

As the inblowing winds come near the heated area, they must 
blow with increased violence, to permit the same quantity of air to 
pass over the constantly nar- 



45° N. 



rowing path. 

Besides the rotary motion of 
the wind, the storm progresses 
or moves in a parabolic path, 
which in the tropics is usually 
directed toward the west, and 
in the temperate zones toward 
the east. This progressive mo- 
tion of the storm, due to the 
combined influences of the in- 
rush of air, the earth's rotation, 
and centrifugal force, is not un- 
like the progressive motion often 
noticed in a rapidly spinning top. 

308. Peculiarities of Cy- 
clones. — Cyclones rage most 
furiously in the neighborhood 
of islands and along the coasts 
of continents. They are most 
powerful near their origin. As 
they advance, the spiral increases 
in size, and the fury of the wind 
gradually diminishes, because 
the amount of moisture in the 
air grows less. The rotary 
motion varies from 30 to 100 

miles an hour. The progressive motion of the calm centre is more 
moderate — from 20 to 50 miles an hour. 

Since the earth's rotation deflects all winds, whatever their direc- 




Janutr; to April. 



Fig. 97.- 



-Chart showing Patli and Di- 
rection of Cyclone. 



212 



PHYSICAL GEOGRAPHY. 



tion may be, to the right in the Northern Hemisphere, and to the 
left in the Southern, it is evident that the direction of the whirl of 
the wind must be opposite to the hands of a clock in the Northern 

Hemisphere, and in the same 



HOKTREBN HENISPUBRS. 




SOOTRERN HEMISPHEBB. 





Fig. 98.— Cause of the Rotation of the Wind. 



direction as the hands of a 
clock in the Southern, as 
will be seen from an inspec- 
tion of Fig. 98. 

The most dangerous part of 
a cyclone lies a little forward 
and to the right of the calm 
centre in the Northern Hemi- 
sphere, and to the left in the 
Southern Hemisphere ; for 
here, not only are the winds 
most violent, but those ex- 
posed to the storm may be 
overtaken by the moving 
centre. 

Oil spread on the water 
notably decreases the violence of the waves. A bag partly filled 
with oil and hung over the vessel to the windward will allow suf- 
ficient oil to drip on the water to diminish the fury of the waves. 
This phenomenon is due to the fact that the oil lubricates the sur- 
face of the water, and thus lessens the friction of the wind upon it. 

The force of the wind in cyclones is tremendous. So furiously does the wind 
lash the water that its temperature is often sensibly raised by the friction. 

The intelligent navigator always endeavors to avoid the centre of the storm, 
since it is the most dangerous part. This he can do by remembering the direc- 
tion of the rotation of the wind in the hemisphere he may be in ; for if, in the 
Northern Hemisphere, he stands so that the wind blows directly in his face, the 
calm centre is on his right, while in the Southern Hemisphere, i< is on his left; 
and, instead of running with the storm, hoping to outsail it, he will boldly 
steer toward its circumference. 

309. Tornadoes, like cyclones, are whirling, travelling storms that 
occur in the United States in the Mississippi Valley and in other 



iSTORMS. 



213 




regious to the east. They are more frequent on the afternoons of 
warm days, and are preceded by the formation of an inverted cone 
or funnel-shaped cloud, as seen in Fig. 99, that descends from a dark 
cloud mass above. This funnel is due to a rotation of the wind 
about its axis, and advances, as a rule, to the east or north-east with 
a loud roaring noise, and is attended by furious winds that destroy 
everything in their path. Tornadoes are of brief duration, seldom 
exceeding an hour or 
even less. They are usu- 
ally connected with extra- 
tropical cyclones. 

310. Water - spouts. 
— When tornadoes or 
whirlwinds occur on the 
water they cause a water- 
spout. Portions of the 
clouds are sometimes 
drawn down from above 
and whirled around in 
the form of an immense 
funnel-shaped mass ; the 
whirl finally reaches 

the water, and a column of spray is thrown up, which unites with 
the mass above and moves over the surface of the water as an im- 
mense pillar. 

311. Temperate-Latitude or Extra-Tropical Cyclones closely 
,resemble tropical cyclones in the following respects : they are 
both attended by travelling areas of low barometer, toward which 
the air is rushing spirally in from all sides ; rain or snow may fall 
over the low-barometer area, the clouds forming on its eastern edge, 
and dissolving or disappearing on its western edge. They differ, 
however, as follows: the areas of temperate-latitude cyclones are 
far greater than those of the tropics, their areas in the United 
States sometimes covering at least one-third of the country ; the 
tropical cyclones are most frequent in early autumn ; the extra* 



Fig. 99.— A Tornado Approaching a Town in 
the Mississippi Valley. Notice the Funnel- 
shaped Cloud Produced hy the Rotary Move- 
ment. 



214 PHYSICAL GEOGRAPHY. 

tropical cyclones may occur at any time, but are most violent in 
winter. 

The cyclones of the temperate latitude are called north-easters in 
the United States, where they are of great importance, since they 
bring the greater part of the rain- and snowfall of the eastern half 
of the country. They are, perhaps, the principal factors in deter- 
mining our thunder-storms and tornadoes. They bring with them 
many of the changes in temperature, such as the hot waves and 
droughts of summer, and the cold waves of winter. 

The following important facts have been discovered in regard to 
the extended storms which occur in the United States : 

(1) All our great storms are attended by an immense whirling of 
the wind, and are, in fact, extra-tropical cyclonesc 

(2) The great north-east storms of our eastern sea-board usually 
originate in the west, in an area of low barometer, somewhere be- 
tween Texas and Minnesota. In the front and rear of this area the 
barometer is high. 

(3) The calm centre of the storm, or the area of low barometer, 
usually moves toward the north-east. The shape of the calm centre 
is longer from north to south than from east to west. 

(4) The storms begin by the winds blowing toward the area of 
low barometer. 

(5) During the prevalence of the storm the winds are north-east, 
east, or south-east ; toward the end, north-west, west, and south-west. 

The causes of temperate-latitude cyclones are not fully known. 
That they are not pure convection phenomena, due merely to an as- 
cending current over a low barometric area, is evident from the fact 
that they are best developed in winter. The wind on the front of the 
eastern side of the storm is warm, and on the rear, or western side, cold. 

312. Warm "Waves are travelling areas of high temperature 
that are situated in front of extra-tropical cyclones, and follow 
them in their progressive movements. They are due to the spiral 
inflow of winds toward the area of low pressure. In the eastern 
United States the inflowing wind comes from the Mexican Gulf or 
the Gulf Stream. Hence its higher temperature. 



STOBMS. 215 

313. Cold "Waves are travelling areas of low temperature situ- 
ated in the rear of extra-tropical cyclones. They are due to the 
spiral inflow of winds toward the area of low pressure. In the 
United States these winds come mainly from the north, and, when 
augmented by an area of high pressure in Canada, produce the 
cold waves. In summer these cold waves bring relief from the 
exhausting warm waves they displace. The winds accompanying 
cold waves are usually dry, because the air becomes warmer 
and relatively drier as it advances. As the terra is employed by 
the United States Signal Service, a cold wave is any fall in tem- 
perature below 32° in the north-west, and below 40° in the south, 
accompanying a change in the temperature of at least 20° within 
twenty-four hours, and this change irrespective of the direction 
or velocity of the wind. When the cold wave is accompanied by 
high wind, a temperature below 32° F., and a blinding snowfall, it 
is called a blizzard. 

314. Hot and Desert Winds. — The passage of any cyclonic or 
low-pressure area is often attended by a great disturbance in the 
winds of neighboring regions, for example, the passage of a cyclonic 
area along the northern shores of the Mediterranean is preceded by 
warm winds from the Sahara. Other hot winds which probably owe 
their origin to cyclonic or low pressure areas are the Sirocco, a hot, dry 
wind that blows over Southern Italy and Sicily ; the /Solano, a simi- 
lar wind that blows over Spain ; the Earmattan, a hot, dusty wind 
that blows over the coasts of Guinea ; the Simoom or Samiel, an 
intensely hot, dry wind from the deserts of Nubia and Arabia, that 
blows over the coasts of Arabia, Nubia, Persia, and Syria ; and the 
Khamsin, a hot wind of Egypt, so called because when once estab- 
lished it generally continues for fifty days. 

During the prevalence of the Simoom, particles of fine sand carried into 
the atmosphere obscure the light of the sun. Becoming intensely heated, 
these particles, by radiation, increase the temperature of the air, which 
sometimes rises as high as 120° or 130° Fahr. When powerful winds prevail, 
dense clouds of sand are carried about in the atmosphere, producing the so-called 
sand-storms. The sand-drifts which are thus formed constantly change theit 
position. 



216 PHYSICAL QEOQBAPHY. 

315. Cold Winds. — In a similar manner the passage of cyclonic 
areas is in many regions followed by cold winds. This is the origin 
of the Northers of Texas and the Mexican Gulf, cold winds that 
blow over Texas and Mexico ; the Etesian winds, cold winds that 
blow over the Mediterranean toward the Sahara ; the Mistral, a cold 
"wind that blows over the valley of the Rhone ; and the Pamperos, 
a cold wind of the Argentine Republic. 

316. Thunder-storms and Thunder-squalls. — Any rain-storm 
attended by thunder and lightning may properly be called a 
thunder-storm.. Thunder-storms are storms that accompany the 
sudden condensation of moisture due to the violent uprush of air, 
such as the heavy rainfalls of the zone of equatorial calms or dol- 
drums, and the heavy rainfalls that occur in the zones of tropical 
calms, the so-called horse-latitudes. Such, too, are the rainfalls 
attending the passage of a tropical cyclone. 

The thunder-storms, however, of the eastern and central parts of 
the United States, and elsewhere, are local disturbances, and differ 
widely in some respects from the above. They occur most fre- 
quently in the afternoon, several hours after mid-day. As the 
dark storm-cloud approaches, a projection of fibrous clouds appears 
at its upper forward edge, while from its lower edge a brief, dust- 
laden wind-squall blows outward along the surface; rain then 
falls, accompanied by thunder and flashes of lightning. These 
thunder-storms are of short duration, seldom lasting an hour. 

Cloud-hursts are due to severe but short-lived thunder-storms, 
accompanied by excessive rainfall. They are frequent in the arid 
districts in the western parts of the United States. 

317. Anti-Cyclones are travelling areas of high barometer. 
They occur in extra-tropical latitudes. They are, it is believed, 
marked by inblowing air above, and a gradual down-settling of the 
air about the central area, which is colder than surrounding dis- 
tricts. They are more frequent in winter than in summer. Gener- 
ally speaking, the velocity is not as great as in cyclones. 

318. Sailing Routes. — A knowledge of the directions of the 
winds and ocean-currents has materially diminished the time required 



STOBMS. 217 

by sailing vessels to go from one port to another. Opposing winds 
and currents often render it advisable for a vessel to begin its jour- 
ney in a direction out of the direct line of the desired port. 

Europe — America. — The Gulf Stream and prevailing westerly winds render 
the passage across the ocean from east to west longer than from west to east. The 
general route, in either direction, varies with the season of the year. 

New York — San Francisco. — After leaving New York the course is consid- 
erably to the east, in order to clear the South American coast in the region of the 
trades. After doubling Cape Horn the course is westward. The zone of the 
north-east trades is entered about 118° W. long. 

America — India — Australia. — In sailing from America to India or to Aus- 
tralia the vessel takes the same route as between Eastern America and San 
Francisco. About opposite Eio Janeiro, however, the routes diverge. On enter- 
ing the Indian Ocean the direction is dependent on the prevailing monsoon. 

Europe — India — Australia. — The vessels either pass through the Mediter- 
ranean Sea and the Suez Canal, or around the Cape of Good Hope. The broad 
expanse of ocean in the Southern Hemisphere, in the zone of the variables, ren- 
ders the westerly winds very steady. Vessels sailing from Atlantic ports of 
America or Europe generally find it preferable to go by the eastward route, 
around the Cape of Good Hope, and return by the westward, route, around Cape 
Horn, thus circumnavigating the globe. 

California— Japan.— The southerly route, from east to west, is aided by the 
north-east trades and the north equatorial current of the Pacific; the northerly 
route, from west to east, is necessary in order to avoid the trade-winds. 

*o>»<oo 

SYLLABUS. 

Atmospheric air is composed mainly of a mixtuie of nitrogen and oxygen, in 
the proportion, by weight, of about 77 parts of nitrogen to 23 of oxygen in every 
hundred parts. It contains also a small quantity of carbonic acid, a variable 
amount of the vapor of water, and small quantities of the elementary substances, 
argon and krypton. Varying quantities of mineral dust are nearly always 
present in the lower strata of the air. 

The oxygen of the air is necessary to combustion and respiration ; the car- 
bonic acid and the vapor of water, to plant-life. 

At the level of the sea the atmosphere presses on every square inch of the 
earth's surface with a force of about 15 pounds. 

The upper limit of the atmosphere has been variously estimated at from 45 to 
200 miles above the level of the sea. 

A barometer is used for measuring the pressure of the atmosphere ; a ther- 
mometer, for measuring its temperature. A self-recording barometer is called a 



218 PHYSICAL OEOGBAPHY. 

barograph ; a self-recording thermometer is called a thermograph ; isobars are 
lines connecting places that have the same mean barometric pressure. 

Climate is the condition of the air as regards heat or cold, moisture or dryness, 
healthiness or unhealthiness. 

The vertical rays of the sun are warmer than the oblique rays : (1) Because 
they are spread over a smaller area of the earth ; (2) Because they pass through 
a thinner stratum of air ; (3) Because they strike the earth more directly. 

The atmosphere is heated: (1) By direct absorption of the rays; (2) By con- 
tact with, or by radiation and reflection from, the heated earth. 

It is the minute particles of dust and water in the air that absorb the greater 
part of the sun's heat. 

Isothermal lines connect places whose mean temperature is the same. 

The mathematical zones are bounded by the parallels of latitude; the phys- 
ical zones, by the isotherms. 

The heat equator, or the isotherm of greatest mean annual temperature, does 
not coincide with the geographical equator. 

The principal modifiers of climate are : (1) The distribution of the land- and 
water-areas ; (2) The diflferences of elevation ; (3) The direction of the slopes of 
the land ; (4) The position of the mountain-ranges ; (5) The nature of the surface ; 
(6) The distribution of the winds and moisture ; and (7) The ocean currents. 

The temperature of the air decreases with the altitude : (1) Because the lower 
layers are nearer the heated earth ; (2) They contain more dust and water par- 
ticles ; (3) They are more directly heated by secondary radiation from the heated 
earth ; (4) They are heated by the condensation of the upper air as it falls to the 
earth's surface. 

Places situated near the sea have a more equable, uniform climate than those 
in the same latitude in the interior of the continent. 

The general system of the atmospheric circulation consists of the following 
currents: (1) The polar currents, blowing from the poles toward the equator; 
(2) The equatorial currents, blowing from the equator toward the poles. 

The direction of these currents is modified by the rotation of the earth. Thus 
modified, the equatorial currents are sonth-west in the Northern Hemisphere, 
and north-west in the Southern. The polar currents are north-east in the North- 
ern Hemisphere, and south-east in the Southern. 

The equatorial currents do not continue as upper currents to the poles : (1) 
Because they become cooled and fall ; (2) From the contracted area of the higher 
latitudes compared with that of the equatorial. 

We distinguish the following wind zones : the zone of equatorial calms ; the 
zones of the trades ; the zones of the calms of Cancer and Capricorn ; the zones 
of the prevailing westerly winds ; and the zones of the polar winds. 

Land and sea breezes are caused by the unequal heating of the land and 
water during day and night; monsoons, by their unequal heating during summer 
and winter. 

Monsoons occur on the coasts of tropical countries within the limits of the 



SYLLABUS. 219 

trade zones. They are most frequent in the Indian Ocean, in the Gulf of 
Guinea, and in the Mexican Gulf and Caribbean Sea. 

Tropical cyclones are caused by the wind blowing in from all sides toward 
an area of low barometer caused by the overheating of the area. 

Storms occur whenever the ordinary equilibrium of the atmosphere is vio- 
lently disturbed by wind, rain, snow, hail, or thunder and lightning. 

Nearly all powerful storms are attended with a rotation of the wind. Such 
storms are known under the general names of Cyclones, Hurricanes, Typhoons, 
and Tornadoes. 

Tornadoes are travelling storms of brief duration, but great violence. 

Temperate-latitude or extra-tropical cyclones are like tropical cyclones travel- 
ling areas of low barometer. Their areas are greater than those of tropical 
cyclones, and they are most violent in winter. 

Warm waves are travelling areas of high temperature situated in front of 
extra-tropical cyclones. Cold waves are travelling areas of low temperature 
situated in the rear of extra-tropical cyclones. 

Hot, desert winds are caused by the heated air from the desert blowing over 
a country by reason of the passage of an extra-tropical cyclone in its vicinity. 
Such winds thus caused by the deserts of Sahara and Arabia are the Harmattan, 
over Guinea ; the Solano, over Spain ; the Sirocco, over Italy ; the Simoom, over 
Arabia, Nubia, and Persia ; and the Khamsin, over Egypt. 

Cold winds are similarly caused by passage of extra-tropical cyclones drawing 
in cold air from the north. 

Anti-cyclones are travelling areas of high barometer. 



KO>»^C 



REVIEW QUESTIONS. 

Of what use is the atmosphere in the economy of the earth ? 

Define meteorology. 

Describe the construction of a barometer ; of a thermometer. 

Define hypsometry ; thermograph ; barograph ; climate. 

Why are the vertical rays of the sun warmer than the oblique rays ? 

What is the characteristic climate of the tropics ? Of the temperate regions? 
Of the polar regions? 

In what different ways does the atmosphere receive its heat from the sun ? 

Define heat equator. 

In what parts of the Eastern Hemisphere is the greatest mean annual tempera- 
ture found? In what parts of the Western Hemisphere? 

What influence is produced on the climate of high latitudes by a preponder- 
ance of moderately elevated land masses? On the climate of the tropics? 

Why should the temperature of the atmosphere decrease with the altitude ? 

Name all the modifiers of climate which prevent the mathematical climatic 
zones from coinciding with the physical climatic zones. 



220 PHYSICAL OEOQRAFHY. 

What is the origin of winds ? 

Name the currents of which the atmospheric circulation principally consists. 

Explain Ferrel's law as to the action of the rotation of the earth on the direc- 
tion of the equatorial and polar currents. 

Name the principal wind zones of the earth. 

Explain, in full, the origin of land and sea breezes. In what respect do mon- 
soons resemble land and sea breezes ? 

Name the principal monsoon regions of the earth. 

Define tropical cyclones. Where do they originate ? In what direction does 
the wind rotate in the Northern Hemisphere ? In the Southern Hemisphere ? 
In what direction does the storm progress in each hemisphere ? Explain the 
cause of the rotation of the wind. What are hurricanes? Typhoons? 

Define extra-tropical cyclones. In what respects do extra-tropical and tropical 
cyclones resemble each other ? In what respects do they differ ? 

Name some hot desert winds caused by the passage of extra-tropical cyclones. 
Name some cold winds so caused. 

Define cold wave ; warm wave. 

Name the important facts which have been discovered respecting the north- 
easters and other severe storms of the United States. 

MAP QUESTIONS, 

Trace on the map of isothermal lines the areas of greatest heat in the Eastern 
Hemisphere. In the Western Hemisphere. 

Show from the map of the isothermal lines wherein the physical torrid zone 
differs in position from the mathematical torrid zone. 

In which hemisphere do the isothermal lines deviate more from the parallels 
of latitude, in the northern or the southern ? 

Trace on the map of the isothermal lines the limits of drift ice. 

What are the mean summer and winter temperatures of Sitka? Of Quebec? 

What causes exist to render the climate of Sitka so much warmer than that 
of Quebec, notwithstanding the difference of their latitudes? 

What are the mean summer and winter temperatures of Mexico, Madras, Singa- 
pore, Berlin, London, Philadelphia, Algiers, Melbourne, and Eio Janeiro? 

What instances can you find on the map of the increase in the mean annual 
temperature of places through the influence of ocean currents? Of winds? Of 
rainfall? Of the decrease? 

Trace on the map of the winds the boundaries of the various wind zones. 

Point out the limits of the monsoon regions of the world. 

What cold wind blows over Texas ? 

Describe the route a vessel would take in sailing from America to Europe. 
From New York to San Francisco. From America to Australia. 



PRECIPITATION OF MOISTURE. 221 

SECTION II. 
MOISTURE OF THE ATMOSPHERE. 



CHAPTER I. 

Precipitation of Moisture. 

319. Evaporation. — From every water surface, and even from 
all masses of ice and snow, water vapor is constantly passing off 
into the atmosphere at all temperatures. This giving off of vapor 
from the surface of water is called evaporation. It is evapora- 
tion which dries the wet earth, when the moisture is unable either 
to run off by surface drainage, or to soak through porous strata. 
Water vapor is invisible, and is about three-fifths as heavy as air. 
Consequently, a cubic foot of moist air is lighter than a cubic foot 
of dry air at the same temperature. Water vapor diffuses readily 
through the air, and is borne by the winds to all parts of the earth. 

About one-half, by weight, of the vapor of the atmosphere is within a little 
over a mile above the mean sea level. 

320. The Rapidity of Evaporation is influenced by the follow- 
ing circumstances : 

(1) The Temperature of the Atmosphere. — The capacity of the air 
for absorbing moisture increases with the temperature. Warm air 
can hold more vapor than cold air. 

(2) The Extent of Surface Exposed. — Evaporation takes place 
only from the surface ; therefore, the greater the surface, the greater 
the evaporation. 

(3) The Quantity of Vapor Already in the Air. — Dry air absorbs 
moisture more rapidly than moist air. All evaporation ceases when 
the air is completely saturated. 

(4) The Renewal of the Air. — During calm weather, the air in 



222 PHYSICAL GEOGRAPHY. 

contact with a water surface becomes more nearly saturated, and so 
lessens evaporation. Gentle breezes, by renewing the air, increase 
the rapidity of evaporation. • 

(5) Pressure on the Surface. — A diminished atmospheric pressure 
increases the rapidity of evaporation. 

The yearly evapoi'ation at latitude 13° N,, at Madras, is 91.2 
inches ; at Boston, latitude 42° N., it is 39.1 inches ; at Great 
Salt Lake, 41° N., it is 80 inches. 

321. The De'W Point. — When the air contains as much vapor as 
it is capable of holding, it is said to be at its dew point. 

The quantity of moisture necessary to saturate a given quantity of air and 
bring it to the dew point varies with the temperature. Cold air requires less 
moisture to saturate it than air whicli is warmer, and, therefore, may feel damper 
than warm air, which may contain more vapor. We thus distinguish between 
the actual humidify, or the amount of vapor actually present in a given volume 
of air. and the relative humidity, or the relation between the amount present and 
that required to saturate the air at the given temperature. 

The humidity of the air is determined by means of an instrument called a 
hygrometer. 

The Hygrometer and the Psyehrometer. — The diagram on page 193 shows 
that the hygrometer consists of a wet and dry bulb thermometer. Since evapora- 
tion produces loss of heat, as the water on the wet bulb evaporates, it will cause 
a loss of heat from the mercury and the wet bulb thermometer will read lower 
than the dry, providing there is a degree of dryness in the air. From the lower 
temperature we can ascertain whether the air is very dry or contains a fair 
amount of moisture. If the air is completely filled with water particles, both 
thermometers will read alike, as there can then be no evaporation. The hair 
hygrometer, the condensing hygrometer, in which the thing directly observed is the 
dew point, and the chemical hygrometer, in which the moisture in a given bulk of 
air is chemically absorbed and weighed, are other forms of this instrument. 

The construction of the psyehrometer is similar to that of the 
hygrometer. The sling psyehrometer is attached to a board, and 
moved swiftly through the air to secure more rapid evaporation. 

No matter how much aqueous vapor a given quantity of air con- 
tains, if its temperature be lowered, it will grow relatively moister 
until, if the fall of temperature he sufficient, its dew point is reached. 
Consequently, in warm weather, the air toward evening, while cool- 
ing from the highest temperature of the day, is growing relatively 



PRECIPITATION OF MOISTURE. 223 

moister, until finally it may reach its dew point ; i. e., become 
saturated with water vapor, and as soon as the temperature falls 
below the dew point, a deposition of moisture will begin, either 
in the liquid or the solid state. 

As a rule, the quantity of moisture in the air decreases from the 
equator toward the poles, and from the coasts of a continent toward 
the interior. It also varies with the character of the prevalent 
winds and the time of the year. 

322. Precipitations. — The invisible vapor may become visible, 
and be precipitated from the atmosjihere either as dew, frost, mist, 
fog, haze, cloud, rain, sleet, hail, or snow. These are called 'precipi- 
tations. 

Law of Precipitations. — In order that any form of precipitation 
may occur, the air mud he cooled below the temperature of its dew 
point. 

323. Distribution of Precipitations. — The quantity of moisture 
in the air depends on its temperature and its vicinity to the sea. 

The amount of precipitation regularly decreases as we pass from tJie 
equator to the poles, and from the coasts of the continents toward the 
interior. 

324. Dew. — If, during a warm day, when the air contains con- 
siderable water vapor, a dry glass be filled with cold water, the 
outside of the glass will soon become covered with small drops of 
water, derived entirely from the air. The moist air which comes 
in contact with the cool sides of the glass has its temperature lowered 
below the dew point, and deposits as vapor the moisture it no longer 
can retain. 

The dew which is deposited during certain seasons of the year on 
plants and other objects on the earth has a similar origin. Objects 
on the earth cool more rapidly than the surrounding air, which 
deposits its moisture on them whenever they lower its temperature 
below the dew point. When the objects are colder than 32° Fahr., 
the dew is deposited as hoarfrost. 

Some recent experiment? of Aitken appear to show that part of the dew 
deposited on the ground, or on vegetation, comes from the ground and from the 



224 PHYSICAL QEOORAPUY. 

plants. Both the ground and vegetation are constantly giving off water, which 
readily evaporates during day time, but collects during cold nights when the 
air is nearly saturated, and evaporation has nearly ceased. 

Dew falls or is deposited more copiously on some objects than on 
others. This is because some objects radiate or give off their heat 
more rapidly than others, and thus, becoming cooler, condense more 
of the moisture of the air. 

More dew is deposited during a clear night than during a cloudy 
one, because objects cool more rapidly when the sky is clear than 
when it is cloudy ; thick clothing keeps the body warm, not because 
the clothes give any heat to the body, but because they are non- 
conductors, and prevent the escape of heat from the body. In like 
manner the clouds, acting as blankets to the earth, prevent its losing 
heat rapidly. 

More dew falls or is deposited during a still night than during a 
windy one. 

The air must remain long enough in contact with cold objects to 
enable them to lower its temperature and collect its moisture. 
Powerful winds prevent this, while gentle breezes favor the depo- 
sition, by bringing fresh masses of air into contact with the cold 
objects. 

In the tropics, during seasons when the sky is clear, the dew is so copious that 
it resembles a gentle rain. 

In the deposition of dew, the moisture is derived from a comparatively thin 
stratum of air in the immediate neighborhood of the cool object. All other kinds 
of precipitations are produced by the cooling of a large mass of air. 

325. Fogs and Clouds. — Whenever the temperature of a large 
mass of air is reduced below its dew point,, its moisture begins to 
collect in minute drops, which diminish the transparency of the air, 
and form fogs, mists, or haze when near the surface, and clouds when 
in the upper regions. Fogs and clouds are the same in their origin 
and composition, and differ only in their elevation. Saze is a name 
applied to the condition of the air when there is a general, but 
comparatively small, loss of its transparency, due to the pressure 
of very minute drops of water. The presence of fine particles of 
mineral dust, or fine smoke particles, also produces a haze. Some 



PRECIPITATION OF MOISTURE. 225 

recent laboratory experiments by Aitken have led him to believe 
that the formation of clouds is dependent on, or at least greatly 
aided by, the presence of dust-particles in the air. The readi- 
ness with which both clouds and rain form in the higher regions 
of the air, where the dust is practically absent, does not appear 
to support this belief. 

Clouds and fogs are formed of minute drops of water, a sub- 
stance about eight hundred times heavier than air. Notwithstand- 
ing their relatively greater weight, they are prevented from settling 
rapidly by the resistance of the air. This is rendered possible by 
the minute size of the drops, which are much smaller than the rela- 
tively heavier dust-particles, which are wafted about by the winds. 
Whenever the drops exceed a certain size, they fall as rain or snow. 
When at temperatures above 32° Fahr., the minute drops of water 
in clouds vary in size from -^^^ to xwo ^^ ^^ ^^^ i^ diameter. 

Clouds or fogs result whenever a mass of air is cooled below the 
temperature of its dew point, which occurs when two bodies of air 
of different temperatures are rapidly mingled, especially if, as is 
usually the case, the warmer of the two bodies is the moister. 
Clouds or fogs disappear on the approach of a dry, warm wind. 
Clouds are higher in the tropics than in the polar regions, and, as a 
rule, are higher during the day than during the night. 

326-7. Classification of Clouds — Clouds assume such a vari- 
ety of shapes that it is difficult to classify them. 

The Cirrus Cloud consists of fleecy, feathery masses of con- 
densed vapor, floating in the higher regions of the atmosphere. 
These clouds are called by sailors cats' tails or mares' tails. From 
their elevation, the moisture is, probably, in the condition of ice- 
particles. Halos, or circular bands of light around the sun, are 
caused by light passing through the ice-particles of cirrus clouds. 

The Cumulus is a denser cloud than the cirrus, and is formed 
'in the lower regions of the air, where the quantity of vapor is great. 
Cumulus clouds generally consist of rounded masses, in the shape 
of irregular heaps, with 'moderately flat bases. They are caused 
by ascending currents of air, which have their moisture condensed 

15 



226 



PHYSICAL GEOGRAPHY. 




Fig. 100.— Cirrus Clouds. 





Fig. 100a.— Cumulus (Woolsack) Clouds. 



L^ 



Fig. 101.— Strato-Cumulus Clouds. 



PRECIPITATION OF MOISTURE. 



227 




Fig. 101a. — The I^^imbus, or Bain Cloud. 




Fig. 102.— Cirro-Cumulus Clouds. 



Fig. 103.— Cumulo-Stratus Clouds. 



228 PHYSICAL GEOGRAPHY. 

by the cold produced by expansion. Cumulus clouds occur during 
the hottest part of the day. Their height seldom exceeds two 
miles. 

The Nimbus, or Storm Cloud, is any cloud from which rain is 
falling. Any of the various forms of clouds may collect and form 
a nimbus cloud. The nimbus is not considered as a distinct form 
of cloud by some meteorologists. 

The Stratus, or Layer Cloud, forms in long, horizontal sheets 
or bands. These clouds are most common in the early morning 
and evening, when the ascending currents are weak. They are 
caused by the gradual settling of the other forms of clouds. The 
stratus cloud sometimes falls to the surface of the earth, and be- 
comes a fog. 

The Cumulo-Stratus is the form produced by the heaping 
together of a mountain-like mass of cumulus clouds ; the base par- 
takes of the nature of the stratus cloud, but the top clearly re- 
sembles cumulus clouds. These clouds differ but little from the 
nimbus, or storm cloud. 

The Cirro-Cumulus is a cirrus cloud, arranged in little rounded 
masses, shaped something like cumuli. They are sometimes called 
"wool sacks," and indicate dry weather. 

Sometimes the cirrus clouds are frayed and torn by air currents. 
At other times they occur in bunches, arranged often in lines, as if 
produced by the waves of the air, the groups of clouds resembling 
a choppy sea. When the sky is speckled with these cloud forms, 
sailors call it the mackerel sky. 

The Alto-Cumulus, or high cumulus, is a dense, fleecy cloud, 
grayish balls being grouped in flocks or rows, frequently so close 
together that their edges meet. 

328. Rain. — When, during the formation of a cloud, the condensa- 
tion of moisture continues, the drops of which the clouds are composed 
increase in size, and, uniting, fall to the earth as rain. As the rain- 
drops fall through the clouds they grow larger by the addition of 
other drops which unite with them. Moreover, they may grow 
larger by the condensation of moisture on their surfaces as they fall 



PRECIPITATION OF MOISTURE. 229 

through very moist air. Raindrops, therefore, are larger when the 
clouds are thick. They are, in general, larger in the tropics than 
in the polar regions, and during the day than at night. In fine rain 
the size of the drops varies from -^ to ^o of an inch in diameter. 
In heavier rains they reach a diameter of -^-^ of an inch and over. 

To produce rain, it is necessary that the temperature of a large 
mass of air be reduced considerably below its dew point. There are 
several ways in which this cooling may be effected : 

(1) By a Change of Latitude. — A warm, moisture-laden wind may 
blow into a cold region. The equatorial currents of air deposit their 
moisture in the temperate and polar zones on account of the chilling 
experienced as they recede from the equator. 

(2) By a Change of Altitude. — An ascending current of air 
carries the moisture of the lower regions into the upper regions, 
where the rapid expansion of both air and vapor, under the dimin- 
ished pressure, chills the air and condenses its moisture. It is mainly 
in this manner that the rains of the tropical region are caused. 

The rains of mountainous districts have a similar cause. A moist 
wind, reaching a mountain-range, is forced by the wind back of it 
to ascend the slopes. Contact with the cold, upper slopes, as well as 
the cold produced by expansion due to elevation, cause condensation 
of the vapor as rain. 

(3) The Mingling of Masses of Cold and Warm Air. — By this 
means heavy clouds and a moderate rainfall may be produced; 
but the precipitation can never be considerable, because the cooler 
air will be warmed by the mixing, and, therefore, will have its 
capacity for moisture increased instead of diminished. 

In all of the methods above mentioned there is an actual motion 
of the moisture-laden air. Rainfall is, therefore, usually an attend- 
ant on cyclonic and thunder-storms, and on other violent movements 
of the air. 

Sleet consists of frozen rain. The word is also sometimes applied 
to a mingling of rain with fine particles of snow or hail. 

329. Distribution of the Rainfall.— The distribution of rain 
may be considered both in regard to its periodicity and its quantity. 



230 PHYSICAL GEOGRAPHY. 

The distributiou of the rain is dependent upon the direction of the 
wind. Each wind zone has a characteristic rainfall. 

The following simple principles determine the rainfall in any par- 
ticular wind zone : 

(1) The equatorial currents are rain-hearing, because they are 
moist; while on their way to the poles, their temperature and con- 
sequent capacity for moisture are constantly decreasing. 

(2) The polar currents are dry, because they are constantly increas- 
ing in temperature as they approach the equator ; hence, they take 
in, rather than give out, moisture. 

The polar currents, when they have reached the zones of the trade winds, 
may bring abundant rains, provided they have previously crossed an ocean. They 
then discharge the moisture with which they are saturated, either by ascending 
or by blowing against the elevations of the continent. 

330. Periodical Rain Zones include the zone of calms and the 
zones of the trades. 

The Zon6 of Calms. — In the zone of calms it rains nearly every 
day. In the early morning the sky is cloudless ; but about the 
middle of the day, as the heat increases, the ascending currents, 
rising higher, begin to condense their moisture ; cumulus clouds 
form, and, increasing rapidly, soon cover the sky, when torrents of 
rain descend during the afternoon or early evening, accompanied by 
thunder and lightning. After a few hours the rain ceases, and the 
sky again becomes clear. In this zone it seldom rains late at night. 
The annual fall in this zone has been estimated at about 100 inches. 

331. The Zones of the Trades. — Since the trades are generally 
dry winds, it is only when their temperature is considerably de- 
creased that they can cause rain. In the zone of the trades, except 
in mountainous districts, and on the windward coasts of a continent, 
the rainfall occurs during the greatest heat of the season, when the 
sun is directly overhead and the ascending currents are powerful. 
Hence, it rains during a few months in summer, when immense 
quantities of water fall ; the remainder of the year is dry. Copious 
dews, however, occur at night. 

The precipitation is not continuous throughout the entire summer. Since the 



PRECIPITATION OF MOISTURE. 231 

rain falls only when the sun is nearly overhead, a brief interval of dry weather 
occurs in regions near the equator, thus dividing the season into two parts ; one, 
during the passage of the sun over the zenith ; the other, on his return to the 
zenith from the adjacent tropic. The tropical cyclones that blow at times over 
portions of the zones of the trades bring with them extremely heavy rains. 

Over the ocean, during most of the year, there is no rain in the 
zone of the trades, although the actual humidity of the air is quite 
high. 

332. The Monsoon Reg-ion of the Northern Indian Ocean. — During the 
prevalence of the winter ruousoon, the north-east trade winds bathe the eastern 
shores of Hindostan in copious rains, while the western shores, shielded by the 
ranges of the Ghauts, are dry. During the summer monsoon, the south-west 
winds bathe the western shores and the southern slopes of the Himalayas in 
heavy rains, while the eastern shores are dry. This monsoon also brings rains 
to the western coasts of the peninsula of Indo-China. 

333. Non-Periodical Rain Zones include the zones of the pre- 
vailing westerly winds and the zone of the polar winds. 

Rainfall in the Zones of the Prevailing "Westerly Winds. — 
The air in these zones is subject to frequent cyclones of the extra- 
tropical type which are attended by plentiful rainfall. These may 
occur at any season of the year. Since extra-tropical cyclones are 
most severe in winter, some parts of the zones have their greatest 
rainfall at this season of the year. In other regions, especially over 
the heated continents, the over-heated areas, producing local storms, 
cause the rainfall to be greater in summer. The annual rainfall in 
these zones varies in different parts from 30 to 80 inches, or even 
more. 

Rainfall in the Zone of the Polar "Winds. — In these zones the 
winters are dry, because the dry, cold polar currents then prevail ; 
but during the summer the equatorial currents sometimes prevail, 
and bring with them dense clouds and fogs, accompanied by driz- 
zling rains. The snows occur mainly in spring and autumn. The 
annual precipitation, including both snow- and rainfall, is somewhat 
less than 15 inches, and in some regions it is less than 10 inches. 
When, as in this case, the snowfall is included, the amount of water 
the melted snow would produce is estimated. 



232 



PHYSICAL GEOGRAPHY. 



Vertical Section. 



All the rain zones, together with their wind zones, follow the sun 
in his annual movements north and south of the equator. 

334. Quantity of Bain, — The quantity of rain which falls in a 
given time on any area is determined by means of an instrument 
called a rain-gauge or pluviometer. 

The rain-gauge as employed by the United States 
Weather Bureau is in the form of a cylindrical vessel 
with a horizontal base, surmounted by a funnel-shaped 
vessel A, called the receiver. Connected with the 
receiver is a vertical glass tube of such smaller diam- 
eter that the rain falling into A mounts in C just ten 
times higher than the actual fall, thus facilitating its 
exact measurement. B is an overflow attachment. The 
rain-gauge is placed in an exposed position, where it is 
free from eddies or whirls. If, during any given time, 
the water in C is one inch deep, then during that time 
the rainfall over the area equals one-tenth of an inch. 
In speaking of the rainfall of a country, the moisture 
which may fall as snow is always included. 

An inch of rain over a surface a square yard 
in area equals in weight 46f pounds ; on the 
surface of an acre it is nearly equal in weight 
to 100 tons. 

The annual rainfall is distributed, as regards quantity, as follows : 
irrespective of the elevations of the surface, 7nore rainfalls in the 
tropics than in the temperate regions, and more in the temperate than in 
the polar regions. The quantity thus decreases with approximate 
regularity from the equator toward the poles. This is caused by a 
similar decrease in the heat and evaporation. 

While the amount of rain that falls decreases from the equator to the poles, 
the number of cloudy or rainy days increases, being greater near the polar than 
in the equatorial regions. 

More rain falls on the coasts of a continent than in the interior, 
because the winds are moister near the ocean. That coast of a 
continent which first receives the prevailing wind has the greatest 
rainfall. 

More rain falls in the Northern hemisphere than in the Southern. 




Fig. 104.— Rain- 
gauge. 



PRECIPITATION OF MOISTURE. 



233 



This is due to the greater extent of the land-area of the Northern 
Hemisphere. 

Mountains receive a heavier rainfall than the plains below, because 
the moist winds, in order to cross the mountains, are forced to ascend 
their slopes, and thus pass into a colder region of the atmosphere. 
Therefore, the sources of rivers are generally found in mountainous 
districts. Mountains are among the most important causes of rain. 

When the mountains are high, the winds may reach the farther 
slopes dry and vaporless. The tropical Andes of South America 
afford an excellent example of this. 

Plateaus, though higher than plains, receive, as a rule, less rain, 
because they are usually surrounded by mountain-chains which 
rob the winds of their moisture. Moreover, the air over a plateau 
is warmer than at a corresponding height in the atmosphere over 
the plains, and therefore fails to condense the moisture. 

77ie rainfall of the Western Continent, both in the tropical and 
temperate regions, is greater than that of the Eastern Continent ; 
thus, in the tropics of the Western Continent, 115 inches of rain 
fall yearly, while the same portions of the Eastern Continent receive 
but 77 inches. In the temperate zones in America the annual rain- 
fall is 39 inches, while in Europe it is but 34 inches. 

The mean annual rainfall at Philadelphia is 46.93 inches. 

The preceding principles find ample illustration in the following table : 

Table op Annual Rainfall foe Wettest and Deiest Yeaes (mainly 

after Tripp). 

Tropics. 

Driest. Wettest. Driest. 

Inches. Inches. Inches. 

283.00 Cayenne, Guiana (John- 
ston) 116.27 

Jubbulpore 94.80 28.80 

Batavia 94.40 52.00 

Calcutta 93.30 43.50 

Madras 88.40 18.40 

Mauritius 75.50 20.70 

Jamaica 40.81 19.01 



Wettest. 
Inches. 

Cherra Pongee, India . 591.46 
San Luis de Maranhao, 

Brazil (Johnston) . . 280.00 
Paramaribo, Guiana 

(Johnston) 229.20 

Kutching (Straits Set- 
tlements) ...... 188.28 

Colombo, Ceylon . . . 139.77 
Bombay 122.00 



159.73 
60.55 
33.90 



234 



PHYSICAL GEOGRAPHY. 



Temperate Zones. 



Wettest. 
Inches. 

New Orleans 110.6 

Genoa 10S.4 

Boston 67.7 

Cincinnati 65.2 

Fort Leavenworth . . 59.6 

New Haven 58.1 

Lisbon 51.0 

Geneva 49.5 



Driest. 
Inches. 

41.9 

28.2 

27.2 

25.5 

15.9 

30.7 

13.5 

20.7 



Wettest. Driest. 

Inches. Inches 

Marseilles 43.0 10.6 

Edinburgh 39.0 13.7 

San Francisco .... 38.8 11.9 

London 35.3 17.3 

Sacramento 34.9 8.4 

Naples 32.6 16.0 

St. Petersburg .... 29.3 12.1 

Paris 27.7 8.3 



Fig. 105 shows a chart of the mean annual rainfall of the earth, 
with the value of the rainfall given in inches. 




T A R C T t C O i! A' N 



MEAN ANNUAL RAINI ALL 

H LESS T«« to INCHEs Uimillllll FROM 60 TO 76 l» 



Fig. 105.— Chart of Mean Annual Rainfall. 

335. Cause of Deserts. — Deserts are caused entirely by the ab- 
sence of moisture. Their soil, though usually finely pulverized, or 
sand-like, does not differ from that of other areas, save in the ab- 
sence of vegetable mould. Thus, neither the nature of its tempera- 
ture nor the character of its soil is the cause of the desert of 
Sahara, since a vigorous vegetation always follows the appearance 



PRECIPITATION OF MOISTURE. 235 

of water on the successful boring of an artesian well. It is prob- 
ably true, that deserts once formed, tend to perpetuate themselves 
by the influence their naked surfaces exert on the rainfall. 

336. Rainless Districts. — In some parts of the world rain falls 
so seldom, or in such limited quantity and at such long intervals, 
that they are known as rainless districts. The most extensive rain- 
less districts are found in the Eastern Continent. 

Desert Belt of the Eastern Continent. — From the western 
shores of Northern Africa, eastward to the Great Kinghan Moun- 
tains in Asia, extends an almost uninterrupted belt of desert lands. 
This belt includes the great Desert of the Sahara^ the Arabian and 
Persian Deserts, and the Desert of Mongolia. The aridity is more 
nearly absolute in the western part of Sahara, and in the desert of 
Arabia, where rain seldom falls. Toward the east, in Persia and 
Mongolia, scanty rains occur. 

The cause of this immense desert tract is to be found in the dry trade-winds, 
which blow over most of the region. Having previously crossed the vast conti 
nent of Asia as upper currents, they arrive at the deserts dry and vaporlesa 
Even that portion of the region which receives the winds from the Mediterranean 
iias but a very scanty rainfall, because any clouds that form are usually soon 
dissipated by the hot air of the desert. 

Persia and Mongolia owe their deserts to their high mountain bor- 
ders, which rob the clouds of their moisture. The high system of 
the Himalayas effectually prevents any of the moisture of the south- 
west winds from penetrating the plateau of Mongolia. 

Arid tracts occur in the Kalahari desert, in Africa, and near the Tropic of 
Capricorn, in Australia. 

Deserts of the Western Continent. — In North Avierica the 
location of the high mountain-ranges near the Pacific prevents 
the passage over them of the prevalent westerly winds with their 
burden of vapor from the Pacific. Their western slopes have an 
ample supply of rain, but the land to the east is very dry. This 
is especially true in the United States, where in Southern California, 
Arizona, New Mexico, Colorado, and neighboring districts, agri- 



236 



PHYSICAL GEOGRAPHY. 



culture practically depends on irrigation. Further to the north the 
rainfall is not so scanty. 

In South America, on the western slopes of the Andes, between the 
parallels of 27° and 23° S., is found the Desert of Atacama. Here 
rain seldom falls, although the ground is occasionally refreshed by 
mists and dews. The cause of the absence of rain is to be traced to 
the high Andes, which condense all the moisture of the trades on 
their eastern slopes, the winds thus arriving at the v.'estern slopes 
dry and vaporless. 

It is questionable whether any desert region is absolutely rainless. 
Even in the Sahara, and in Arizona and Lower California, there is 
at times a scanty rainfall. 



-»-o>»^c 



CHAPTER II. 



Hail, Snow, and Glaciers. 

337. Hail falls when considerable differences of temperature 
exist between higher and lower strata of very moist air, and the 
moisture is suddenly condensed in the presence of great cold. Usu- 
ally, several layers or bands of dark, grayish clouds precede 
these storms. Hail falls most frequently in summer, near the 
close of an excessively warm day, as a not uncommon accompani- 
ment of the thunder-storms of the United States. 

Structure of the Hailstone. 
—If a large hailstone be placed 
on a hot surface and left until one- 
half is melted, its structure may 
readily be examined. Concentric 
layers, similar to those of an onion, 
will be noticed, arranged around 
a central nucleus, sometimes of 
ice and sometimes of snow. Hail- 
stones are more or less oblately 
spheroidal in shape. Their gen- 
eral weight varies from a few grains to several ounces, but they have been known 
to weigh several pounds. 




Fig. 106.— Structure of a Hailstone. 



HAIL, SNOW, AND QLACIEBS. 



237 



Origin of Hail. — The cause of hail is not fully understood, and 
several theories have been framed to account for it. 

Perhaps the least objectionable theory regards hail as the result of a convec- 
tional disturbance of the air, which results in the wind rotating, as in a cyclone, 
only the axis of the whirl is horizontal instead of vertical. Drops of frozen 
rain, or sometimes pellets of snow, caught in the whirl, are covered succes- 
sively with layers of snow and ice, as they are successively carried into colder 
or warmer regions. 

Thunder and lightning are the invariable attendants of hailstorms, and some 
authorities have attributed the formation of the stones to successive electrical 
attractions and repulsions of snowflakes between a snow and a rain cloud. 
There does not, however, appear to be any evidence of this. 

338. Snow. — When the moisture of the air is condensed at any 

temperature below 32° Fahr., the vapor crystallizes as it condenses, 

and snowflakes are formed. 

Snowflakes grow, as they fall, by 
condensing additional moisturs from 
the air. They are larger in mild than 
in cold weather. They assume quite a 
variety of forms, but are built up by 
various groupings of minute rhombo- 
hedrons of ice. The star-shape is the 
most common. 




Fig. 107. — Snow-crystals. 



If the temperature of the air 
near the surface is much warmer 
than 32° Fahr., any snow that is 
formed in the upper regions will 
melt before reaching the ground. 
Hence, in the temperate zones, 
as a rule, snow reaches the sur- 
face only in winter, wbile in the 
tropics it never reaches the surface, except near the summits of 
lofty mountains. 

It is a mistake to suppose that the fall of snow is greater in regions near the 
poles than elsewhere ; for in high latitudes there is comparatively little moisture 
in the air. The snowfall is heaviest in the cool temperate regions. 

339. Effect of Snow-covered Areas on the Temperature of the Air. 
— A snow-covered area produces a marked effect in chilling the air over it. 
Since snow is a non-conductor of heat, it gains practically no heat from the 



238 PHYSICAL OEOQRAPHY. 

earth, aud, since it is a good radiator and poor absorber of heat, it rapidly 
loses its heat and becomes cold. A comparatively thin layer of snow, therefore, 
say a foot or so, once formed, tends to remain throughout the winter. Such 
snow-fields tend to retard early vegetation. This retarding of the drainage 
of the winter snowfall is of great value in regions of scanty rainfall, such as 
exist in the Western United States, since it renders easier the storage of the 
winter fall for purposes of irrigation. 

340. Snow Line. — Regions of Perpetual Snow. — The snow 
which falls on mountains slowly moves down the slopes by the weight 
of the snow above. The distance it will move before completely 
melting depends on a number of circumstances. The lower limit 
of permanent snow is called the snow line. Above it are the regions 
of perpetual snow, where the ground is covered with snow through- 
out the year. 

The height of the snow line depends: 

(1) On the Amount of the /Snowfall. — The greater the fall, the farther 
down the mountain the snow will move before completely melting. 

(2) On the Temperature of the Valley. — The warmer the valley 
the higher the snow line. The snow line is, therefore, highest in 
the tropical regions, and lowest near the poles. 

(3) On the Inclination of the Mountain Slope. — The steeper the 
elope, the more rapidly the snow will move, and the farther it 
will go before melting ; therefore, the lower the snow line. 

According to Guyot, the snow line, with some exceptions, is about three miles 
above the sea in the tropics ; rather less than two miles in the temperate lati- 
tudes; and less than a mile near the northern extremities of the continents; 
while still farther north, on the polar islands, the snow line is but a few hundred 
feet above the sea. 

SNOW LINE. 

Ewrope.— Norway, Lat. 70° N 3,400 feet. 

" 60° N 5.500 " 

" Alps, Lat. 46° N. (south side) 9,200 " 

" " " " (north side) 8,800 " 

^sia.— Altai Mountains, Lat. 50° N 7,000 " 

" Himalayas, Lat. 31° N 17,000 " 

^/Hca.— Kilimandjaro, Lat. 3° S 16,000 " 

North America. — Eocky Mountains, Lat. 43° N. . . . 12,467 " 

South America. — Andes, Ecuador, Lat. 1° S 15,800 " 

" " " 54° S 3,700 •' 



HAIL, SNOW, AND GLACIERS. 239 

The snow line is generally lower in a moist than in a dry atmosphere, be- 
cause of the greater fall of snow from moist air. As a rule, that slope of a range 
which is exposed to the prevalent wind has a lower snow line than the opposite slope. 
The position the slope occupies in relation to the vertical rays of the sun also 
exerts an influence on the height of the snow line. 

341. Glaciers are masses of snow and ice, which move slowly 
down the higher mountain valleys. Their upper parts are formed 
of soft snow ; their lower portions of clear, hard ice. Their origin 
is as follows : The weight of the huge snow-fields, which form above 
the snow line, forces the mass slowly down the slopes to regions 
where the waste exceeds the supply. The pressure, due to the 
weight of the layers, especially where the mass is forced through 
a contraction in the valley, squeezes out the confined air, to which 
snow, in great part, owes its white color, and the lower part of the 
glacier thus becomes changed into a compact mass of clear ice. 
The alternate thawing and freezing to which the mass is subjected 
also contribute to the change from snow to ice. 

In the lower parts of the glacier the ice is marvellously clear. In large masses 
its color is of a deep azure blue. In the middle portions of the glacier the ice 
is coarse and white. The higher region of but partially changed snow is called 
the neve region. Here the snow occurs in coarse white grains. The process of 
formation is a continuous one. The neve region is supplied by fresh falls of 
snow, which replace these forced down the slopes. 

34:2. Types of Glaciers. — Russell divides glaciers into three 
types ; namely, 

(1) Alpine Glaciers, or those which occur in highest mountain 
regions, such as the glaciers of the Alps, the Himalayas, the Rocky 
Mountains, the Mountains of Scandinavia, etc. Alpine glaciers 
have their origin on the summits and flanks of lofty mountains, 
and form ice streams that descend their many valleys. 

(2) Piedmont Glaciers, or those formed by the union of the Alpine 
glaciers on the plains adjacent to the mountain defiles. These gla- 
ciers may be compared, in the ice drainage of the land, to lakes in 
the water drainage. 

The Malaspina glacier at the southern base of Mt. St. Elias and 
neighboring mountains in Alaska, is an example of a Piedmont 



240 PHYSICAL GEOGRAPHY. 

glacier. It covers an area of some 1500 square miles and varies in 
thickness from 1000 to 1500 feet. 

(3) Continental Glaciers, or glaciers of vast extent that cover 
large parts of continents. The glaciers of Greenland and of the 
Antarctic regions are of this class. 

343. Drainage of Snow and Ice. — Glaciers resemble rivers, since 
they receive the drainage of their basins through the solid material 
which flows into them ; their motion, however, is much slower. 

Several glaciers often unite and flow on as a single stream ; but 
their solid condition prevents the intermingling which occurs in 
rivers, and the separate streams may generally be distinctly traced 
throughout the remainder of their course. Like rivers, the top 
and middle portions move more rapidly than the sides or bottom, 
owing to the diminished friction. The motion of the glacier is 
not necessarily dependent on the natural slope of the land. In 
the cases of continental glaciers the ice mass moves up slopes, as 
well as down, the direction of motion being determined by the pitch 
of the upper surface of the ice. Some glaciers, however, are devoid 
of motion, being, in this respect, like motionless or stagnant water. 

344. Peculiarities of Glaciers. — -The surface of the glacier is 
often comparatively smooth ; but when irregularities occur, either in 
the direction of the valley or in the slope of its bed, the glacier is 
broken into deep fissures, called crevasses. Crevasses are most nu- 
merous on the sides, from which they extend either obliquely up the 
stream, or directly across, in deep transverse fissures. The former 
are generally due to a bend in the valley, one side being compressed 
and the other extended ; the latter, to steep and abrupt descents in 
the bed. Crevasses, therefore, are rapids in the ice stream. 

Crevasses vary in breadth from mere crevices, that a knife-blade can scarcely 
penetrate, to yawning chasms over 100 feet in width. The depth of the wider 
crevasses is generally profound. Their vertical walls afford a convenient oppor- 
tunity for studying many peculiarities of formation. Looking down the walls of 
the crevasses, the ice appears of a deep azure blue. The surface ice is a dirty white. 

The crevasses gradually disappear below the cause of disturbance, the frac- 
tures mending by regelation ; i. e., a property which fragments of moist ice have 
of becoming firmly cemented together when their surfaces are brought into 
contact under pressure. 



HATL. >\njV. AXD GLACIERS. 



240a 




rig. lOTa. — The Icy Surface of a Great Swiss Glacier. 



240b 



PHYSICAL GEOGRAPHY. 




Fig. 107b.— Snow Field and Glacier with Lateral Moraines in the Alps. 







Fig. 107c. — Two Glaciers Joining, Showing the Formation of a Medial Moraine. 



HAIL, SNOW, AND GLACIERS. 



241 



The water derived from the melting of the ice issues from a cav- 
ernous arch at the end of the glacier. The volume of the issuing 
stream, which is often considerable, is, of course, dependent on the 
temperature, and is greater during the warm months of the year. 
Many rivers, such as the Rhone and the Rhine, in Europe, and the 
Ganges, in Asia, have their origin in these glacier streams. 

The distance the glacier extends below the snow line depends on the mass 
and velocity of the ice and the rapidity with which it melts. When the winter 
snows are light, and the following summer unusually warm, the end of the 
glacier retreats up the mountain. On the contrary, heavy snowfalls in winter, 
followed by a cool summer, permit the end of the glacier to advance far into the 
valley below. 

345. "Work of Glaciers. — All along the borders of the valleys, 
stones and dirt roll down the declivities, and, accumulating on the 
surface of the moving mass, 
are carried with it to a lower 
level. These accumulations 
of dirt and stones are called 
moraines; they are named 
according to their position 
as follows : 

(1) Lateral Moraines, or 
those which collect along 
the sides of the glacier. 

(2) Medial Moraines, or 
those situated in some cen- 
tral portion of the glacier, 
and resulting from the junc- 
tion of two or more lateral 
moraines, where two or more 
glaciers have united in a 
single stream. 

(3) Terminal Moraines, or 
the crescent-shaped ridges 

formed at the end of Alpine glaciers on the melting of their 
extremities. 

16 




Fig. 108.— Moraine and Glacier, 
Canadian Rockies (Phreaner). 



242 PHYSICAL OEOQBAPHY. 

The terminal moraines formed at the margin of piedmont and 
continental glaciers are called frontal moraines. 

The material transported by glaciers is known as glacial drift 
Only a portion of the debris carried forward by the glacier is 
deposited in the terminal or frontal moraine. Most of the drift is 
arranged beneath the ice as a ground moraine. This includes the 
substances frozen in the ice mass and pushed along with it over 
its bed. 

346. Glacial Deposits and Sediments. — The mineral matter 
carried forward and deposited by glaciers may be divided into 
two classes : 

(1) Glacial Deposits, or those made directly from the ice mass, 
such as moraines, drumlins, etc. 

(2) Glacial Sediments, or those deposited from streams of water 
escaping from the glacial ice. 

347. Erosion. — Such immense masses of ice must deepen con- 
siderably the valleys through which they move. Where they have 
deserted their former valleys, evidences of their previous existence 
are to be found not only in the long lines of unstratified rocks, boul- 
ders, and mud, left by their moraines, but especially in the deep 
grooves, or scratches, cut in the bottom or sides of the valleys by 
rocks imbedded in the moving ice mass. These scratches are par- 
allel, and show the direction of the motion. 

The water which issues from the terminal cave is deeply charged with a fine 
sediment, the result of erosion. This sediment is exceedingly fertile, and, spread 
out hy the rivers on the flood-grounds, becomes a source of agricultural wealth. 

348. Geographical Distribution of Glaciers.— Some of the 
principal glacial regions of the world are as follows : 

Europe. — In the Swiss Alps, where there are two regions — 
those of Mt. Blanc and those of Monte Rosa. The Mer de Glace 
(sea of ice), one of the best known of the European glaciers, descends 
from the slopes of Mt. Blanc. It is formed by the confluence of three 
glaciers — du Geant, de Lechaud, and de Talefre. Glaciers also 
occur in the Bernese Alps, in the Pyrenees, in the Austrian Alps, 
and in the Caucasus Mountains. 



HAIL, SNOW, AND GLACIERS. 



243 



North America. — In Alaska, in the mountain-ranges on its south- 
ern borders, adjacent to the Pacific, especially around Mount Logan, 
19,500 feet, and St. Elias, 18,025 feet, or the many adjacent peaks, 
there are extended glaciers of the Alpine type. The Taku 
glacier, which dis- 
charges into Taku In- 
let, and the Muir gla- 
cier, which discharges 
into Glacier Bay, are 
tidewater glaciers, and 
form numerous ice- 
bergs. The Malaspina 
glacier, at the southern 
base of Mt. St. Elias 
and neighboring peaks. 
has an area of, approx- 
imately, 1500 square 
miles. To the west lies 
the Bering glacier. 
Both of these are, in their lower parts, of the Piedmont type. Gla- 
ciers also occur in the south-western parts of the Dominion of Can- 
ada and in the north-western part of the United States. 

Greenland. — A vast ice sheet or continental glacier, with an area 
of about 600,000 square miles, covers nearly all Greenland. It is 
the largest existing glacial mass in the Northern Hemisphere. 
The ice flows outward in all directions in glacial streams, many 
of which reach the ocean and form numerous icebergs. Humboldt 
Glacier, in Lat. 79° 31' N., is one of the most important. It is 
some 40 miles in length, and from 200 to 300 feet above the sea-level. 
Vast snow-fields, with numerous glaciers, are also found on Grinnell 
Land, and on the islands west of Baffin's Bay and in Davis' Strait. 

Besides the above, glaciers occur in South America, in Tierra del 
Fuego, and in parts of the Andes ; in Asia, in the Himalayas ; and 
in New Zealand. Extensive glacial regions also occur in the Ant- 
arctic regions. 




Fig. 109.— The Mer de Glace (Zeller 



HAIL, SNOW, AND GLACIERS. 245 

349. Icebergs. — When the glacier extends into the sea, the base 
is undermined by the ^Yarmer waters of the ocean, and great frag- 
ments are broken off by the waves, forming floating mountains of 
ice, called icebergs. Icebergs are particularly numerous in the 
North Atlantic, into which they descend from the extensive Arctic 
glacial region. 

350. Varieties of Icebergs.— Where the surface of the ice mass 
above the water is exposed to the air, the ice is of dazzling white- 




Pig. 111.— Taku Glacier. 

ness ; below the water, where it is protected from the air, it has the 
characteristic deep-blue color of glacial ice. 

In a region where icebergs are being separated from the glacial 
mass three types of bergs are seen in bright sunlight : 

(1) Dazzling White Bergs, or those where the lighter white ice 
projects only above the surface. 

(2) Blue Bergs, or where unequal melting has caused the inver- 
sion of the bergs, thus bringing the blue ice above the surface. This 
change of position is due to the bergs becoming bottom buoyant. 



246 PHYSICAL GEOGRAPHY. 

(3) Dirt-bedecked Bergs, due, possibly, either to fragments of 
bottom ice or to parts of the berg that formed the sides of 
crevasses. 

The ice floes of the polar seas have their origin in the snow which 
falls into the cold water, remaining partially dissolved and subse- 
quently freezing, thus adding to the thickness of the ice formed. 

351. Glacial Epoch. — At the beginning of the Quaternary Period, 
the climate of northern latitudes grew colder, pi'obably owing to an 
increase in the elevation of the Northern Continents. At the same 
time the air became moister, so that the accumulation of snow was 
favored. The glaciers of the mountainous district, therefore, moved 
down their valleys, and spread gradually over the Northern Conti- 
nents, covering them with an ice sheet or continental glacier. This 
epoch is known as the glacial epoch. In North America, where it 
was best marked, this ice sheet extended generally north of the line 
marked on the map shown in Fig. 110 ; it existed also in some of 
the high mountainous districts in the south. Alaska appears to 
have escaped this ice sheet. 

When the ice sheet finally melted, it left evidences of its former 
presence by extensive erosion in some regions, and by the depo- 
sition of eroded materials in others. Over vast areas are found 
thick layers of stones, gravel, sand, and clay, both unstratified and 
roughly stratified, deposited either by the ice alone, or by the ice 
aided by the water derived from its melting. These deposits are 
known as glacial drift. 

352. Varieties of Glacial Drift Deposits. — Drift deposits occur 
in various forms : 

(1) Moraine Deposits. — These assume forms that depend on the 
character of the moraine, whether terminal, lateral, medial, ground, 
etc. Moraine deposits are sometimes roughly stratified. 

(2) Till Sheets, or deposits of tough clay, containing more or less 
sand, stones, and boulders of various sizes, devoid of any regular 
arrangement. The till is believed to have been deposited by the 
ground moraine of the ice sheet, and to have been formed largely 
from the bed rock on which it rests. 



HAIL, SNOW, AND GLACIERS. 247 

Till deposits cover large areas in most of the northern parts of 
the United States that were covered by the ice sheet of the glacial 
epoch. In some regions, such as New England, the boulders and 
large stones are so numerous that farming is practically impossible. 
In other states, such as Ohio, and most of the states as far west as 
the Dakotas, the till is not so rocky, and is, consequently, more fer- 
tile. Till sheets are usually unstratified. 

The accumulations of till and other drift deposits often assumed 
characteristic shapes called drumlins, eskers, and kame&. 

Drumlins are low, rounded, oblong hills, probably formed under 
the ice sheet. They correspond to sand-bars or mud-flats in rivers, or 





Fig. 112.— Drumlin. 

to sand-hills or dunes on the land. They are very common in New 
England, in New York, and in other states west to the Dakotas. 

Eskers are long, tortuous ridges of gravel or sand, deposited 
by the streams that flowed through winding tunnels under the ice. 
Karnes are rounded hillocks piled up by the sub-glacial waters. 

Outside the glaciers, when the streams descended valleys, they 
formed deposits called valley trains. 

353. Characteristic Drainage. — The drainage of a drift-covered 
region possesses all the characteristics of immaturity, and lake- 
basins are, consequently, numerous. Before the drainage systems 
were fully established on the new surface, the irregularities were 
occupied by lakes. A drift-covered region is, therefore, a lake 
region. The finer drift materials, settling in these lakes, form 
extremely fertile plains on the disappearance of the water. 

354. Glacial Groovings or Scratches. — Where the drift does 



248 



PHYSICAL OEOQRAPHY. 




not cover the ground, evidence of the former presence of the ice is 
found in parallel cuttings, scratches, or groovings in the surface of 

hard rocks, due 
to the action of 
stones embedded 
in the ice mass. 
These scratches, 
as shown in Fig. 
113, are fre- 
quently crossed 
by other marks, 
showing a change 

in the direction 
Fig. I13.-Glacial Scratches. ^^ ^^^ ^^^^ ^^^^ 

probably, to a change in the level or inclination of the surface of 

the ice mass. 

355. Boulders, or erratic blocks, that have been transported 

by the ice and left,' on its 
melting, in far-distant re- 
gions, are very common. 
Some single specimens of 
these weigh several thou- 
sand tons. 

356. Fiords. — Certain 
varieties of shore lines are 
called fiords. Fiords are 
deep inlets separating lofty 
headlands. These inlets 
often extend from 50 to 
100 miles into the inte- 
rior, whila numerous high 

rocky islands lie off the shore. The coast of Norway presents a 

typical example of such a shore line. 

The origin of fiords appears to be as follows : Deep valleys were cut by glacial 
action during a period of elevation. Through subsequent subsidence, and the 




Fig. 114.— Boulders. 



HAIL, SNOW, AND GLACIERS. 249 

disappearance of the glacier, the sea penetrated far into the valleys, leaving 
the summits of the mountains as numerous islands. The depths of the fiord 
valleys may be judged by the fact that some of them on the American coast, 
between Maine and Labrador, are shown by soundings to extend more than 
3000 feet below the level of the sea. Since the bottom of these channels is prob- 
ably covered with drift, their real depth is much greater than that indicated by- 
soundings. 

Dana names the following as fiord coasts — Maine, Labrador, 
Newfoundland, Greenland, British Columbia, Alaska, Norway, 
Western South America south of 41° S. Lat., Tasmania, and South 
Australia — and calls attention to the fact that they are all in glacial 
latitudes, as indicating their origin. Fiords are, therefore, another 
proof of the existence of ancient glacial systems. 

357. Extensive Disturbances in River Channels and Drain- 
age Areas were caused either by the attending changes of level or 
by the presence of the ice sheet. The direction of flow of many 
streams was reversed, and the outlets of many lakes changed. 
Lake Winnipeg, for example, on the melting of the ice mass, instead 
of emptying into the Hudson Bay, as at present, emptied into the 
Mississippi River. Temporary lake basins, some of which were of 
enormous area, were formed by the damming up of the drainage 
area by the retreating ice mass. Lake Agassiz is an example. 
This lake, formed during the retreat of the ice sheet, was nearly 
700 miles long from north to south, and, probably, 250 miles, 
broad. Its surface was, probably, 700 feet above the present level 
of Lake Winnipeg. The waters of this lake discharged south, 
through the now extinct Warren River, into the Mississippi. Its 
boundaries are shown in Fig. 110. 

Other examples of prehistoric lakes are found in Lakes Bonne- 
ville, 19,750 square miles in area, and Lahontan, 8422 square milas 
in area. They were formed by increased rainfall in districts where 
arid conditions now prevail. They appear to have had their origin 
in the changes of climate that produced the ice sheet of the glacial 
epoch. Their locations are shown in Fig. 110. 



250 PHYSICAL GEOGRAPHY. 

CHAPTER III. 
Electrical and Optical Phenomena. 

358. Elementary Electrical Principles. — Although we are 
ignorant of the real nature of electricity, we are well acquainted 
with the principles which control its action. 

An electrical flow or current is always produced by the action of 
the force that sets electricity in motion, called electromotive force 
(usually contracted E. M. F.). In order to set electricity in motion 
a conducting path or circuit must be provided. E. M. F. is meas- 
ured in units called volts. 

When a body, such as a piece of glass, is rubbed against a bit of 
cat skin, both the glass and the skin are charged with electricity, 
that is, are electrified, or have an E. M. F. developed in them by 
friction. If the glass be touched by a knuckle of the hand, an elec- 
tric spark passes, and the glass is discharged, or a current of electricity 
is momentarily produced. Generally speai^ing, when an E. M. F. is 
properly applied to a circuit, an electric discharge is sent through 
the circuit. 

359. Electric Sources. — There are various ways in which E- 
M. F.'s and, consequently, electric discharges or currents, may be 
produced. Any device for producing E. M. F. is called an electric 
liource. 

Energy is required to produce an electric current, and, therefore, 
is expended in all sources that are connected with working circuits. 

Some of the more important electric sources are voltaic batteries, 
dynamo-electric machines, frictional electric machines, and thermo- 
electric piles. In voltaic batteries, chemical energy is transformed or 
converted into electric energy. In dynamo-electric and frictional 
electric machines, mechanical energy is converted into electric energy. 
In the thermo-electric piles, heat energy is converted into electric 
energy. 

In every electric source the electricity is assumed to flow out of 
the source at one place, and to return to the source, after passing 



ELECTRICAL AND OPTICAL PHENOMENA. 251 

through the electric circuit, at another place. These places are 
called poles, the positive (+) pole being the pole from which the 
electricity leaves the source, and the negative ( — ) pole, the pole 
at which it returns to the source. 

360. Conductors and Non-conductors. — All electric circuits 
offer a measurable resistance to the passage of an electric discharge. 
Electric resistance is measured in units called oh)is. The resistance 
of a circuit depends both on the nature of the materials of which it 
is composed and on their lengths and areas of cross-section. The 
longer the circuit, and the smaller its area of cross-section, the 
greater its resistance. 

Some substances, such as most metals, charcoal, acids, aque- 
ous solutions, and various animal and vegetable substances, are 
good conductors of electricity ; others, on the contrary, such as gums, 
resins, glass, silk, and dry air are poor conductors, or are, rela- 
tively, non-conductors. Consequently, when it is desired that a cir- 
cuit should possess a small resistance, it is made as short as possible, 
of good conducting material, such as copper wire, and of as heavy a 
cross-section as may be required. When a circuit is necessarily of 
high resistance, a high E. M. F. is necessary in order to enable a 
large current to pass through it. The rate at which electi'icity 
passes through a circuit is called the electric current, and is meas- 
ured in units called amperes. An ampere is the current which 
would pass through a circuit whose resistance is one ohm under an 
E. M. F. of one volt. 

361. Atmospheric Electricity. — Electric excitement, or an 
electric charge, is always present in the atmosphere. The electricity 
of the air is usually positive, although it often changes rapidly to 
negative on the approach of clouds or fogs. It is feeblest within a 
tew feet of the surface, and increases with the elevation above the 
general surface of the earth. 

Origin of Atmosplieric Electricity. — The exact causes of the electricity of 
the atmosphere are unknown. It has been ascribed to a variety of circumstances, 
the chief of which are evaporation and condensation ; unequal heating of the 
earth by the sun's rays ; combustion ; animal and vegetable life ; and the frictioR 
of winds against each other, or against the earth's surface. 



252 



PHYSICAL GEOGRAPHY. 



362. Lightning and Thunder. 




Fig. 115.— Lightning Flash (John M. Justice.) 



Lightning occurs when the 
electric charge of a cloud 
discharges to the earth or 
to a neighboring cloud. 
The discharge is attended 
by a vivid spark, called 
lightning. The destructive 
effects of lightning are due 
to the discharge which 
occurs between the cloud? 
and the earth. 

The heat of the dis- 
charge vaporizes the rain^ 
drops, and enormously 
expands the air, produc- 
ing, on their subsequent 
condensation and cooling, 
a partial vacuum, which 
is further increased by 
the momentary pushing 
aside of the air by the 
discharge. The surround- 



ing air rushing violently into this vacuum produces the sound called 
thunder. 

The electromotive force of the lightning flash is enormously higher than 
that produced by artificial means, and must be equal to many millions of volts. 
This high potential is due to the enormous decrease in the surface of a single 
rain-drop as compared with the combined surfaces of the thousands of smaller 
drops which have coalesced to form it. 

363. Varieties of Lightning. — There are six varieties of light- 
ning : zig-zag or chain, sheet, heat, globular, volcanic, and multiple or 
ribbon lightning. 

Zig'-zag Lightning- probably owes its forked shape to the resistance of the 
air. The zig-zags are not angular, but curved, as may be seen from an examine 
tion of the photograph of lightning flashes as shown in Fig. 115. The air-parti- 



ELECTRICAL AND OPTICAL PHENOMENA. 



253 



cles, being crowded together in tie patli of the spark, the lightning darts to one 
side, where the air is not so dense. 

Sheet Lig'litning' usually accompanies thunder-storms, and appears as an ex- 
panded flash, which illumines 
the clouds. 

Heat Lig'htning', or light- 
ning without thunder, is gen- 
erally seen near the horizon 
during hot weather. It is, 
probably, caused by the re- 
flection of lightning from a 
storm below the horizon. 

Globular Lig-htning-. — ■ 
On rare occasions the light- 
ning appears in the form of 
a globe of light, which re- 
mains stationary in the air 
or moves slowly through it. 
Its cause is unknown. 

Volcanic Lig'htning. — 
During volcanic eruptions 
flashes of lightning often oc- 
cur near the craters. Volcanic 
lightning is probably caused 
by the rapid condensation of 
water vapor emitted with the 
ashes and lava. 

Multiple or Ribbon 
Lightning' is a rare form, in which the discharge takes the shape of a number 
of parallel discharges, giving the flash the appearance of a ribbon. Fig. 116 shows 
a photograph of such a discharge in which there are fourteen distinct discharges 
separated by dark spaces. The cause is unknown. 

364. Lightning Rods, invented by Franklin, protect the build- 
ings on which they are placed by quietly discharging the electricity 
from the overhanging cloud. They generally ensure this by an 
opposite electric discharge passing from the earth up the rod, and 
neutralizing the charge of the cloud. When struck by a flash, the 
rods safely conduct the discharge to the ground. Unless they are 
placed in good metallic connection with the earth, and with all con- 
ductors near them, they are sources of danger rather than of protec- 
tion. 




Fig. 116.— Multiple or Ribbon Lightning. 

(Photographed by John M. Justice.) 



254 



PHYSICAL GEOGRAPHY. 



_-«^ia's-^---l: 




365. St. Elmo's Fire. — When the atmosphere is highly charged 
with electricity, faint tongues of fire are often seen on the extremities 
of tall bodies, such as the masts of ships, steeples, etc., due to an elec- 
tric discharge, known as the 
brush-discharge. This phe- 
nomenon is known as St. 
Elmo's fire, and is harmless. 

366. The Aurora Bore- 
alis, or northern light, is a 
phenomenon of great beauty, 
occurring in the sky of high 
I latitudes in both the Northern 
" and Southern Hemispheres. 
It appears in a variety of 
forms ; at times huge pillars 
of fire move rapidly across 
the heavens, or the northern 
sky is lighted as by a drift- 
ing storm of luminous snow. 
The most common appearance, 
however, is that of an arch of fire, from which streamers flash toward 
the zenith. 

Auroras are most frequent in high latitudes, though not in the 
immediate vicinity of the poles. 

Auroras are caused by the passage of electricity through the rare air of the 
upper regions. The proofs are as follows : During the continuance of an aurora, 
the telegraph wires show the presence of an unusual electrical disturbance, and 
the magnetic needle is subject to frequent oscillations ; the same phenomena may 
be produced by the passage of an electrical current through rarefied gases, as 
in Geissler tubes — different colors arising from its passage through different 
gases. Moreover, the close accordance of the periods of greatest frequency of 
auroras with similar periods of sun spots would seem to suggest their depend- 
ence on the magnetic conditions of the sun and the earth. 

367. Magnetism. — Magnets are bodies which have the power 
of attracting particles of iron, or the opposite poles of other 
magnets. 



Fig. 117.— St. Elmo's Fire. 



ELECTRICAL AND OPTICAL PHENOMENA. 



255 



All magnets possess an atmosphere of influence surrounding 
them, called the magnetic field. The magnetic field is traversed 
by magnetic flux, or lines of magnetic force, which come out of the 
magnet at one point and enter it at another, thus forming a mag- 
netic circuit. The points where the lines come out and enter the 
magnet are called poles ; the former being the positive or north pole, 
and the latter, the negative or south pole. 

The general direction of these lines may be shown by sprinkling 
iron filings over a sheet of paper held horizontally over a magnet 
and then gently tapping the paper. 
The filings will come to rest in the 
general direction of the magnetic lines, 
as shown in Fig. 118. 

Magnets are either natural or arti- 
ficial. Lodestone, a species of iron 
ore composed of oxygen and iron, is 
naturally magnetic. Pieces of hard- 
ened iron or steel may be magnetized 
by rubbing them with a lodestone, 
thus producing what are known as s^vllWfl^ 
artificial magnets, often called perma- 
nent magnets, because they retain 
their magnetism. By passing elec- 
tric currents around a piece of soft 
iron there is produced what is called 
an electro-magnet. Such a magnet loses 
its magnetism as soon as the electric current ceases to pass, and 
is, therefore, sometimes called a temporary magnet. All magnet- 
izable substances become magnetized when they are brought into 
a magnetic field. 

If a magnetized bar or needle be suspended at its centre of grav- 
ity so as to move freely in a horizontal plane, it will, after a few 
oscillations, come to rest with one of its ends pointing nearly to the 
geographical north pob of the earth. This end of the magnet is 




256 



PHYSICAL GEOGRAPHY. 




Fig. 119.— The Magnetic Needle. 



called its north pole, the opposite end, its south pole, and the magnet 
itself, a magnetic needle. 

368. Magnetic Attractions and Repulsions. — If a magnet is brought near 

a magnetic needle, as in Fig. 119, 
attraction or repulsion will ensue — 
repulsion, when the poles are of the same 
name; attraction, when they are of oppo- 
site names. Thus, when a north pole 
is approached to a north pole, or a 
south pole to a south pole, they 
repel each other ; but when a north 
pole is approached to a south pole, 
or a south pole to a north pole, they 
attract each other. If the approach- 
ing magnet is powerful, it will de- 
flect the magnetic needle, although 
several feet distant from it; and 
if placed permanently in this posi- 
tion, the magnetic needle will no 
longer point to the north, but will turn toward the disturbing magnet. 

369. The Magnetic Properties of the Earth. — The magnetic 
needle points to the north for the same reason that the opposite 
poles of magnets point to each other when they are suflBciently 
near. The entire earth acts as a huge magnet, with its poles in the 
neighborhood of its geographical poles, and the needle points toward 
these poles on account of their magnetic attraction. 

The earth, like all magnets, possesses a magnetic field. Lines of magnetic 
force come out at its north magnetic pole, pass around its surface through the air, 
and enter the earth at its south magnetic pole. A magnetic needle, placed in 
the earth's field, if free to move, will come to rest with the earth's lines of 
force entering at its south pole and passing out of its north pole. That pole 
of the needle which points to the geographical north is, therefore, of opposite 
magnetic polarity to the earth's polarity in the Northern Hemisphere. 

370. Origin of the Earth's Magnetism. — The exact cause of 
the earth's magnetism is unknown. Currents of electricity circu- 
lating through any conductor render it magnetic. Electric currents 
are generated in nearly all substances when they are unequally 
heated. The earth appears to owe its magnetism to the circulation 
around it of currents of electricity, produced, most probably, by 



ELECTRICAL AND OPTICAL PHENOMENA. 



256a 



the unequal heating of different portions of its surface by the sun's 
rays. These currents would follow the sun in its apparent motion 
from east to west. Since the earth's magnetism appears to have its 
remote cause in the sun's heat, variations in the earth's temperature 
should be followed by corresponding variations in the intensity of 
its magnetism. This is found to be the case. 

Magnetic storms, or unusual variations in the earth's magnetism, 
have been noticed to correspond with outbursts of solar activity, as 
manifested by the unusual occurrence of sun spots. 

The Mariner's Compass.— 
The compass is a slender bar of 
magnetized steel, so constructed 
as to balance on a pivot and turn 
■ freely upon it as well. Usually it 
is armed with a sliding weight, 
so adjusted that it exactly coun- 
terbalances the dip or vertical 
force, thereby keeping the needle 
in a horizontal position. 

On land the compass is of but 
little practical use except in rough 
surveys. On the sea, however, 
it furnishes the only means by 
which a vessel may be kept continually on her course. For this 
reason the mariner's compass is constructed with the greatest care 
and precision. The needle, which consists of one or more slender 
bars of steel, is fastened to a circular card subdivided into thirty- 
two parts, on which are printed the cardinal directions. These are 
called points of the compass. The compass box is so mounted in 
the binnacle that no matter what may be the motion of the vessel, 
the box always retains a horizontal position. The compass of Lord 
Kelvin consists of a battery of six or more very slender magnets 
held in a skeleton frame. The latter is so light that the friction 
on the bearing is imperceptible. This compass is used in the Brit- 
ish navy, and by most of the great ocean liners. 




Fig. 119a.— The Compass Card. 



256b 



PHYSICAL GEOGRAPHY 




Fig. 119b.— A Pocket Compass. 



Along nearly every travelled ocean 
route, the variation of the compass 
changes day by day. On the regular 
routes of the transatlantic liners, the 
variation Increases from about nine 
degrees at New York to more than 
thirty-five degrees at the crossing of 
the 40th meridian. It then decreases 
to about twenty degrees at Liverpool. 
In arctic regions, where the horizontal 
element of force is so weak, and the 
dipping force so strong, sailing by 

compass is a very difficult matter. Not only does the variation 

change rapidly over short courses, 

but the needle becomes exceedingly 

sluggish. 

The Dipping Needle.— The com- 
pass needle can swing only to the 

right or left. If it were hung so that 

it could swing up or down it would 

usually not lie level, but slant, or 

"dip," in one direction or the other. 

A needle thus hung is called a clijy- 

ping needle, and is said to show the 

Magnetic Dip. 

Magnetic Poles and Meridians. 

— The magnetic poles are those 

places on the earth's surface where 

the lines of magnetic force are 

vertical. They are supposed to 

change their positions slowly. The 

north magnetic pole is in Canada at 

about latitude 70i° N. and longitude 





" rJ!^ 






\ 


I 



97° W. The other is in the antarctic 
regions in latitude 72° 25' S., and 



Fig. 119c.— A Ship's Binnacle or 
Compass Stand. 



ELECTRICAL AND OPTICAL PHENOMENA. 



257 



longitude 155° 16' E. The magnetic meridian of any place is an 
imaginary plane drawn through the zenith, and passing through 
the magnetic north point and magnetic south point of the horizon, 
as observed at that place by the pointing of a horizontally-sus- 
pended compass needle. The angle between the magnetic meridian 
and the geographical meridian of a place is called the magnetic 
declination of that place. In order that ships may steer by the 
compass, magnetic charts must be prepared, and the declination at 
different places accurately measured. 

371. Magnetic Declination. — Since the earth's magnetic poles 
do not coincide with its geographical poles, the magnetic needle 
does not, except in a few localities, point to the true geographical 




Fig. 120.— Declination Chart. 

(West Declination is represented by the continuous lines ; East Declination by 

the dotted lines ; the Agones by the heavy lines.) 

north, but to the east or to the west of it. This deviation from the 
true north is called the declination or variation. Its value is east or 
west, accordingly as the needle points to the east or i,he west of the 
true or geographical north. The amount of this variatioa differs in 
different parts of the earth. 

17 



268 PHYSICAL QEOGRAPHT. 

372. Isogonal Lines. — Lines connecting places which have the 
Bame declination are called isogonal or isogonic lines. Lines con- 
necting places where the needle points to the true north, are called 
agones, or lines of no declination. 

The direction of the isogonal lines is shown in tha declination chart, the 
figures near the lines giving the value of the declination in degrees. The agone 
in each hemisphere is marked 0. In the New World it enters South America 
near Eio Janeiro, curves around the Antilles, passes near Washington, D. C, 
through the western part of Hudson Bay, and enters the magnetic pole near 
Boothia Felix. The agone, in the Old World, passes through the west of Aus- 
tralia, near the western coasts of Hindostan, through Persia, the eastern part of 
the Caspian Sea, and through the White Sea, in Europe. The oval curves in 
Eastern Asia seem to indicate a secondary magnetic pole. In nearly all of 
Europe, in the whole of Africa and Arabia, in eastern North and South Amer- 
ica, and in nearly all of the Atlantic and Indian Oceans, the declination is west. 
It is also west along part of the eastern shores of Asia, around the secondary 
magnetic pole. In the other parts of the world the declination is east. 

373. The Inclination or Dip of the Needle. — The lines of 
force of the earth's magnetic field are, in most places, inclined to 
the earth's surface. The position of the needle is, therefore, hori« 
zontal in but few localities. In most places, one end of the needle 
is inclined to the earth. This is called the inclination or dip of the 
needle. In the Northern Hemisphere, it is the north pole, and in 
the Southern, the south pole, that is inclined. 

374. Magnetic Equator; Isoclinal Lines. — The nearer we 
approach either magnetic pole the greater is the angle of dip. At 
either pole, the needle points vertically downward ; midway between 
the poles, or at the magnetic equator, the needle is horizontal. 

Lines connecting places which have the same angle of dip are called isodi'Mi 
lines. They correspond in a remarkable manner with the isothermal lines. 
This seems to show the dependence of the intensity of magnetism on the dis- 
tribution of the sun's heat. 

375. Variations in the Earth's Magnetism. — The intensity 
of the earth's magnetism is by no means constant, but varies at 
difierent hours of the day, at difierent days in the year, and at 
different cycles, or long intervals of time. Magnetic variations are, 
therefore, either diurnal^ annual, or secular. Besides these there axe 



ELECTRICAL AND OPTICAL PHENOMENA. 259 

irregular variations, which attend so-called magnetic storms that 
occur during periods of unusual solar activity, as indicated by the 
prevalence of an unusual number of sun spots. 

During the variations of the earth's magnetism, the value of the declination 
and inclination of the needle varies. Since the value of the declination varies, 
t/he position of the earth's magnetic poles must change. In the secular varia- 
tions, as shown by a study of declination charts for many years, the magnetic 
needle, at a certain place, pointed more and more to the east, following the 
change of the poles. After a long period it became stationary, and then began 
to move slowly to the west. 

Thus, in 1580, the magnetic declination in London was 11° 18' E. The needle 
was then slowly moving eastward. In 1663, the declination became zero, the 
needle pointing due north and south. It then began moving west, reaching its 
greatest declination, 24° 30' W., in 1818. It has since been moving to the east, 
being, in 1901, about 15° 32' W. 

376. Optical Phenomena are caused by changes in the direc- 
tion, intensity, or composition of sunlight during its passage through 
the atmosphere. 

Sunlight, when passed through a prism, is dispersed or separated 
into a great number of different colored lights. The following seven 
groups of colors are prominent : violet, indigo, blue, green, yelloic, 
orange, and red. These are called the prismatic colors, or, collec- 
tively, a spectrum. They differ in the ease with which they are 
refracted, or turned out of their course, in passing from one medium 
to another of different density. The above prismatic colors seen in 
the spectrum are named in the order of their refrangibility, begin- 
ning with violet, the most refrangible, and ending with red, the 
least refrangible. 

377. Rainbows are arches of the prismatic colors, caused by the 
dispersion of the light during its passage through the falling drops 
of rain. The rays entering the drops are reflected from the interior 
surfaces farthest from the sun, and emerge separated into the pris- 
matic colors. Rainbows are seen when the observer stands with his 
back toward the sun. They are largest when the sun is nearly set- 
ting. A secondary bow sometimes occurs outside the primary, 
with the order of its colors reversed. It is caused by the light 
which is twice reflected from the back of the drops. 



260 PHYSICAL GEOGRAPHY. 

378. The Sunset Tints of the Sky. — As the sun sets, its disl^, 
is of an orange or red color, because most of its blue rays hare been 
scattered, and only the orange and the red rays reach the eye. 
Hence the horizon is colored by orange and red tints as the sun sinks. 
Some of the sunset colors are due to refraction of the light through 
the denser and moister lower layers of air. The sunset glow of rose 
and purple, seen shortly after sunset, is due to the presence of dust 
particles in the air. 

379. The Blue Color of the Sky is due to the fine dust par- 
iicles suspended in the air, to minute drops of water, or to minute 
ice crystals. The blue color is purer in clear weather, and is deeper 
in the higher regions of the air. This, probably, is because the 
suspended particles are finer in the higher regions and in clear 
weather. 

380. Halos and Coronae are rings of prismatic colors surround- 
ing the sun and moon. 

Halos are caused by the presence in the air of small crystals of 

ice or snow. Parhelia, or 

^^ ~~j7^ ^^^ ^-i^ "'- -^^^^._ mock suns, and Paraselenae, 

==_^ ^ -^S^ ^^ mock moons (bright spots 

which somewhat resemble 

suns and moons), are fre- 

^ quently seen where the com- 

^ plicated circles of halos in- 

I tersect each other. Coronae 

^g^ / ^l^^^ s J are circles of light, seen most 

^ - s=s==^ J frequently around the moon. 

7-^ They are caused by the pres- 

S*' ence of a small quantity of 

- ,^^ .- -^_ s!^^-,J^:'''r^"7^^^!!^ condensed vapor in the air. 

Fig. 121.— Halo. They usually indicate 

changes in the weather. 

381. The Mirage is a general term applied to the appearance 
which objects present when viewed by means of rays of light that 
have passed through strata of air, which gradually increase or de- 



ELECTRICAL AND OPTICAL PHENOMENA. 261 

crease in density. In this way the objects appear either inverted or 
erect, but always out of their true position. Sometimes the objects 
appear repeated, one image being seen above the other. The 
mirage occurs both over water and land. It is caused by the turn* 
ing of the rays of light out of their original direction. 

The Mirage of the Desert occurs over hot, arid surfaces, whenever 
the strata of air increase rapidly in density from the surface upward. 
The rays of light from distant objects, such as trees, are reflected 
from one of the lower layers of air, and, entering the eye of the ob- 
server, appear to come from inverted objects, which seem to be sur- 
rounded by a sheet of water. The images of real trees are seen, but 
out of their true situation, so that when the observer reaches the 
place he finds neither trees nor water. 

The mirage frequently occurs on the sea. Vessels that are too far 
below the horizon to be directly seen, become visible by refraction. 
This phenomenon is called looming. The vessels are seen both erect 
and inverted, and sometimes appear suspended in the clouds 
Islands, too distant to be directly seen, sometimes become visibl« 
from the same cause. 

SYLLABUS, 

The rapidity of evaporation increases : (1) With the temperature of the 
atmosphere ; (2) With the extent of surface exposed ; (3) With a decrease in 
the quantity of vapor already in the air ; (4) With the renewal of the air ; and 
(5) With a decrease of the pressure on the surface. 

When air can hold no more moisture in an invisible state, it is said to he satu-' 
rated or at its dew point. 

Whenever the air is lowered below the temperature of its dew point, its moist- 
ure is deposited as dew, frost, fog, cloud, mist, haze, snow, hail, sleet, or rain. 

More dew is deposited on clear nights, when the wind is moderate, than on 
eloudy nights, when the wind is high. 

In fogs, mists, and clouds the vapor is condensed as minute drops of water. 

The formation of clouds is aided by the presence of dust particles in the 
atmosphere. 

The primary forms of clouds are the cirrus, the cumulus, the nimbus, and the 
stratus. The secondary forms of clouds are the cirro-stratus, the cirro-cumulus, 
and the cumulo-stratus. 



262 PHYSICAL GEOGRAPHY. 

Eain falls whenever tlie temperature of a mass of air is lowered considerably 
below the temperature of its dew point. This reduction of temperature may 
occur : (1) By a change of latitude ; (2) By a change of altitude ; (3) By the 
intermingling of moist cold air and moist warm air. 

As a rule, the equatorial currents bring rain, the polar currents, drought. 

In the zone of calms, it rains nearly every day during the hottest part of 
the day, or in the afternoon, when the ascending currents are strongest. 

In the zone of the trades, it rains during the summer. 

In the zone of the prevailing westerly winds, cyclones are frequent, and are 
accompanied by a plentiful rainfall. 

In the- zone of the polar winds, the winters are clear ; snows and drizzling 
rains occur in spring and autumn. 

An inch of rain on the surface of a square yard is equal in weight to 46.75 
pounds ; an inch on the surface of an acre, to a weight of about 100 tons. 

The quantity of rain decreases from the equator to the poles, and from the 
coasts of the continents toward the interior. 

More raiu falls on mountains than on plains ; more on plains than on plateaus ; 
more in the Northern than in the Southern Hemisphere. 

The rainfall of the Western Continent is greater than that of the Eastern. 
In the tropics of the Western Continent, the annual rainfall is 115 inches ; in 
the Eastern Continent, only 77 inches. 

Deserts are caused by the absence of rain. 

The desert belt of the Eastern Continent extends from the western shores of 
}Jortheru Africa eastward to the Great Kinghan Mountains in Asia. It includes 
the Sahara, the Arabian and Persian Deserts, and the Desert of Mongolia. 

In the Western Continent, the western slopes of the Pacific mountain-ranges 
have an ample supply of rain. The western slopes of the Andes, between Lat. 
27° and 23° S., are almost entirely devoid of rain. 

Hail falls when the moisture is suddenly condensed by cold. 

Snow falls when the vapor is condensed at temperatures at or below 32° 
Fahr., under conditions favorable to gradual crystallization while condensing. 
Sleet is frozen rain. The snow line is the lower limit above the sea where snow 
remains throughout the year. 

The height of the snow line depends: (1) On the amount of the snowfall ; (2) 
On the temperature of the valley ; (3) On the inclination of the slopes. 

Glaciers are immense masses of ice, formed by the snow which accumulates 
on the slopes of mountains above the snow line. Glaciers move slowly by gravity 
down the mountain slopes, bearing with them accumulations of dirt and stones, 
called moraines. Moraines are : (1) Lateral ; (2) Medial ; (3) Terminal ; (4) Ground ; 
(5) Frontal. Glaciers are found in the following mountains : The Alps, the Pyre- 
nees, the Caucasus, the Scandinavian, the Himalayas, in some of the mountains 
of the northern, north-western, and western parts of North America, in the 
Andes, in the mountains of New Zealand, and elsewhere. Glaciers are of three 
types: (1/ Alpine; (2) Piedmont; (3) Continental. 



SYLLABUS. 263 

When glaciers descend into the sea, the waters undermine them, and detach 
huge masses, called icebergs, which float away to great distances. 

As regards their appearance, icebergs may be : (1) Dazzling white ; (2) Blue; 
[3) Dirt-bedecked. 

At the beginning of the Quaternary Period, a change occurred in the climate 
of the earth, by which all the northern continents were covered with 
glaciers. 

The glacial drift occurs as: (1) Moraine deposits; (2) Till sheets. These 
deposits assume various forms, such as drumlins, eskers, kames, and valley trains. 

The following are fiord coasts : Maine, Labrador, Newfoundland, Greenland, 
British Columbia, Alaska, Norway, Western South America south of 41° S- Lat., 
Tasmania, and South Australia. 

The unit of electromotive force is called a volt ; the unit of current is called an 
ampere; the unit of resistance is called an ohm. Comparing the flow of elec- 
tricity to that of a current of water in a pipe, the volt corresponds to the pres- 
sure causing the flow, the ohm to the friction or other resistance opposing the 
flow, and the ampere to the quantity of the flow per second. 

Lightning results when the electricity of a cloud discharges to the earth or 
to a neighboring cloud. There are six forms of lightning : zigzag, sheet, heat, 
globular, ribbon, and volcanic. 

When the air contains an unusually great quantity of electricity, faintly 
luminous balls called St. Elmo's fire are seen on the extremities of tall objects. 

Auroras are caused by the passage of electricity through the rare air of the 
upper regions of the atmosphere. 

The earth acts like a huge magnet. It possesses a magnetic field, and has 
lines of magnetic force entering its south magnetic pole in the Northern Hemi- 
sphere, and coming out of its north magnetic pole in the Southern Hemisphere. 

The magnetic needle points to the north, from the action of the magnetic 
■poles of the earth. The cause of the earth's magnetism is not certainly known. 
It is probably due to electrical currents which circulate around it. 

Magnetic storms, or unusual variations in the earth's magnetism, correspond 
with outbursts of solar activity, as manifested by the unusual appearance of 
sun spots. 

The deviation of the magnetic needle from the true north is called its decli' 
nation ; the deviation from a horizontal position, its inclination. Both declination 
and inclination are subject to diurnal, annual, and secular variations. 

Isogonal lines connect places which have the same declination. Isoclinal 
lines connect places which have the same inclination. Isoclinal lines are nearly 
coincident with the isothermal lines. 

Optical phenomena are caused by changes in the direction, intensity, or com- 
position of sunlight during its passage through the atmosphere. 

Rainbows are caused by the action of light on falling raindrops. Halos are 
caused by snow crystals; Coronae, by minute particles of water in the air; 
Mirage, by the rays of light being turned out of their original direction. 



264 PHYSICAL GEOGRAPHY. 

REVIEW QUESTIONS* 

What do you understand by evaporation ? 

Name the circumstances upon which the rapidity of evaporation depends. 

Define dew point. 

What condition is necessary in order that the invisible moisture of the atmoi 
sphere may become visible in any form of precipitation ? 

Under what circumstances is dew deposited ? 

Why is more dew deposited on a clear night than on a cloudy one ? Why ij 
more dew deposited on a still night than on a windy one ? 

Under what circumstances are fogs, or mists, produced ? How do fogs or mists 
differ from clouds ? 

What influence on the formation of clouds is believed to be produced by the 
presence of dust particles in the atmosphere? 

What is the condition f f the particles of water which form the clouds ; are 
they minute drops, or hollow vesicles? 

Describe the appearance of the cirrus cloud. How does its height compare 
with that of other clouds ? 

During what parts of the day are stratus clouds most common ? To what do 
they owe their banded appearance ? 

Describe the cumulus cloud. During what part of the day is it most common? 

Name three conditions under which rain may be caused. By which are the 
heaviest rains generally produced ? 

Are the equatorial currents likely to bring rain or drought? Why? The 
polar currents? Why? 

Name the periodical rain zones. 

When does it rain in the zone of calms? 3n the zone of the trade-winds? 
Why? 

Describe the rainfall in the zone of the prevailing westerly winds. In the 
aone of the polar winds. 

Describe the construction and operation of a rain-gauge or pluviometer. 

Why should more rain fall on a mountain than on the lowlands at its base? 
Why should more rain fall on the coasts of a continent than in the interior ? 

Compare the mean annual rainfall of the tropics of the Eastern and Western 
Continents. Of the temperate regions of America and Europe. 

Name the rainless districts of the Eastern Continent. Of the Western Con- 
tinent. 

What is the cause of the almost total absence of rain in these districts ? 
•Under what circumstances is hail produced ? 

Define snow line. Upon what does the height of the snow line depend? At 
what height above the sea-level is it found in the tropics? In the temperate 
regions? In the polar zones? 

How are glaciers formed ? Name three varieties of glaciers. In what respects 
do glaciers resemble rivers? 



SYLLABUS. 265 

Name some rivers which take their origiu in the melting of glacial ice. 

Define lateral, medial, terminal, frontal, and ground moraines. 

Explain the manner in which fiord valleys were formed. What is the prob- 
able origin of lakes in glacial districts ? 

Name some of the European mountain-systems which contain extended gla- 
cier regions. Name two Asiatic mountain-ranges which contain such regions. 

How are icebergs formed ? Is the ice of which icebergs are composed salt or 
fresh ? 

What are ice floes? State their origin. 

Into what two general classes may glacial deposits be divided ? 

Define drumlin, esker, kame, and valley train. 

Name some of the evidences of the former existence of glaciers in any country. 

Describe the Glacial Epoch. 

Explain the origin of Lake Agassiz ; Lakes Bonneville and Lahontan. 

How is an electrical flow or current produced ? 

Define volt; ohm ; ampere ; circuit. 

Under what circumstances does lightning occur? What is the cause of the 
accompanying thunder ? 

Name six varieties of lightning. By what are auroras caused? 

Why does the magnetic needle point to the north ? 

What is believed to be the cause of the earth's magnetism? 

Define isogonal lines ; isoclinal lines. 

With what lines are the isoclinal lines nearly coincident? 

Explain the phenomena of the rainbow. 

What is the cause of the sunset tints of the sky ? Of the blue color of the sky? 

What are halos and coronae ? By what are they caused ? 



MAP QUESTIONS, 



Trace on the map of the winds the portions of the world included in the zone 
of calms. 

Trace in a similar manner the portions included in the zones of the trades, and 
in the zones of the prevailing westerly winds. 

Why should the eastern shores of tropical South America be moist, and the 
IPestern dry ? 

To what peculiarity of position does Northern Africa owe its scanty rainfall ? 

Trace on the declination chart the agone, or line of no declination, in the 
Western Hemisphere. Trace the line of no declination in the Eastern Hemi- 
sphere. What smaller line of no declination exists in this hemisphere ? 

Notice that in the Western Hemisphere the isogonal lines all meet in a point 
near Hudson Bay ; what does this meeting indicate ? 




Fig. 121a.— Great Slave Lake, Dominion of Canada. 

PART V. 

PLANT LIFE, ANIMAL LIFE, AND 
MINERALS. 



►o>©=jo 



The variety and luxuriance of life on the earth are far greater 
than is at first apparent. Besides the larger animals and plants, 
myriads of microscopic forms inhabit the land, the water, and 
the air. From the burning sands of tropical deserts to the eternal 
snows of the poles, widely differing forms of plants and animals 
occur, each peculiarly fitted for its particular conditions of growth. 

An organic form differs in many respects from one that is inor- 
ganic. An organic form, such as an animal or a plant, has its origin 
in a germ ; grows from nourishment taken into its structure ; has a 
regular development in growth by successive stages, from birth to 
maturity, when it reproduces its kind and passes on to decay and 
death. 

266 



PLANT GEOQBAPHY. 267 

An inorganic form, such as a crystal, grows by accretions or 
additions from outside its body, does not reproduce its kind, has no 
regular development or growth, being perfect from its first existence, 
and has necessarily neither decay nor death. 

*oJ«Ko« 

SECTION I. 
PLANT LIFE. 

^J»<o*' 

CHAPTER L 
Plant Geography. 

382. Living- Matter. — All life, whether vegetable or animal, 
consists of various groupings of cells. Cells are globular masses, 
formed of a peculiar jelly-like matter called protoplasm, composed of 
various complex combinations of carbon, oxygen, and sulphur, called 
proteids. At its beginning, all life consists of a minute germ cell, 
filled with more or less transparent protoplasm, and containing a 
darker, opaque spot called the nucleus. Examined by a sufficiently 
powerful glass, all living protoplasm is seen to be in constant mo- 
tion, currents passing thi'ough the diflferent parts, in somewhat 
definite directions. 

In all the higher forms of life, as the germ cell develops, it multi- 
plies, and various organs appear, peculiar to the form of life from 
which the germ cell was derived. All living bodies contain organs, 
and living matter is, therefore, sometimes called organic matter, to 
distinguish it from non-living, or inorganic matter. 

Science has not yet disclosed the nature of the change whereby non-living 
matter is converted into living protoplasm. To produce living matter the inter- 
vention of already living matter is, so far as is known, absolutely necessary. 

383. Intermediate Position of Plants. — Protoplasm forms an 
essential part of both plants and animals. Plants alone, however, 
possess the power of mnnufacturing protoplasm directly from inor- 



268 PHYSICAL OEOORAPHY. 

ganic or non-living matter. Plants prepare food for animals, who 
consequently, are dependent on plants for their existence. Both 
plants and animals are consumers of the proteid compounds. Plants 
alone are producers. In the scale of existence, therefore, plants 
occupy a position intermediate between minerals and animals. 

384. Photosynthesis. — Only plants containing green coloring- 
matter, or chlorophyll, possess the power of preparing their own food- 
supply directly from the materials obtainable from the soil or from 
the air. Plants devoid of chlorophyll, such as mushrooms, toadstools, 
and fungi generally, are unable to do this, and are dependent on 
other plants for their existence. By far the greater number of 
plants are included in the first class. 

When an ordinary green plant takes in the raw material which 
forms its food : i. e., mainly carbon dioxide and water, a recombina- 
tion of the elements of these substances usually takes place in the 
leaves under the influence of the sunlight. This process is called 
photosynthesis. As a. result, various carbohydrates, or combinations of 
carbon and hydrogen, are formed, the oxygen of the carbon dioxide 
beino- liberated. The proteids are subsequently formed from the car- 
bohydrates, by combination in different proportions with nitrogen, sul- 
phur, and other elements derived from the soil. The food thus manu- 
factured by the plant is either carried directly to parts of the plant 
where work is being done, or the excess is stored in some part. Most 
plants produce more food than they need, and it is on this extra 
food that animals live. 

385. Plant Geography treats of the distribution of plant life 
over the earth. The plants of any section of country, taken collec- 
tively, are called its flora. 

Plant geography diflFers essentially from botany. Botany arranges plants into 
classes, according to peculiarities in their organs of growth and reproduction. 
Plant geography considers vaunts only in reference to their appearance, by which 
they give a distinct character to the vegetation of a country, or to their general 
usefulness to man. 

In this limited view, all the minuter differences in structure or organization 
are passed over, the general form being the main geographical element of a plant. 
and the element with which physical geography is principally interested. 



PLANT Gl ?^TIAPE7. 269 

386. Soil. — In various ways th^ reck masses are broken up into 
more or less finely divided waste, which forms the basis of the soil in 
which plants grow. Usually, there is added to the rock waste a vege- 
table humus or mould, containing tl e decaying remains of animals 
or plants. This vegetable mould is gradually accumulated during 
many years. The principal agencies by which the solid rock is 
broken up or disintegrated are weathering, erosion, corrosion, and 
glacial action. Some soils are formed in place, while others are 
transported, often for considerable distances, from their origin. 

Soils may be considered : 

(1) In regard to their chemical composition ; 

(2) In regard to their physical properties ; that is, to the extent 
to which they absorb and retain their water supply. 

Coulter divides soils into the following classes : 

(1) Rock, that is, uncrumbled rock, on which certain plants only 
ean exist ; 

(2) Sand, which possesses a very small water capacity unless it 
rests on a bed of clay, in which case its water capacity is great ; 

(3) Lime soils ; 

(4) Clay, which possesses a great water capacity ; 

(5) Humus or vegetable mould, which is rich in decaying animal 
and vegetable matter ; 

(6) Salt or alkaline soils. 

From a mere geographical standpoint, the nature of the soil is 
far from being the most impori.nt element in the distribution of 
vegetation, for, even when a soil is absent, if the other requisites 
of light, heat, and moisture are present, the simpler vegetable forms 
soon appear, and slowly prepare, even on a bare, rocky surface, a soil 
which is able to sustain species, which develop more and more 
highly with the development of the soil. 

387. Conditions Requisite for Plant Growth.— Plants require 
for their growth certain conditions of light, heat, and moisture; and 
as the requisite amount of each of these varies with different spe- 
cies of plants, we find in every climatic zone a characteristic flora. 
The soil must contain those mineral ingredients which form a part 



270 PHYSICAL QEOOBAPHY. 

of the structure of the plant, and must contain them in a condition 
in which they can be readily assimilated by the plant. 

In considering the conditions requisite for plant growth, reference 
must be had not only to the actual temperature existing in any 
region, but also to its distribution throughout different parts of the 
year. 

The temperature limits under which plants can exist vary from 
0° to 122° F. Certain plants can grow even in the waters of hot 
springs. In studying the temperature effect on plants, we must 
consider not only the temperature of the air, but also the tempera- 
ture of the soil in which the plants grow, and in this connection 
the soil cover must also be considered. A cover of snow or leaves 
has the effect of reducing the extremes of temperature. 

In considering the quantity of water which falls as rain, or the 
quantity present in any soil, reference must also be had to the water 
level in the soil. In some soils the water level is only a short 
distance below the surface ; while in others, such as sandy soils, it 
is often a considerable distance below the surface. The water in 
the soil consists either of free water, which can be drained away, 
or of water which adheres to the soil. 

388. Moisture, Heat, and Light are the prime essentials of 
vegetation, and it is on their distribution that the distribution of 
vegetation is principally dependent. 

389. Plant Groups, or Societies. — Plants may be divided into 
groups, or societies, according to the quantity of water they require 
for their vigorous growth. These plant groups or societies are as 
follows : 

(1) Water-plants, or such as grow only in water or in very wet 
soils. 

An example of a water-plant is to be found in the sargassum, a 
species of sea-weed that accumulates in the sargasso seas in mid- 
ocean. The buoyancy of this weed is increased by air contained in 
ball -shaped floats, as shown in Fig. 122. 

(2) Drought plants, or those which can exist only in very dry soil 
with dry air ; these include plants capable of withstanding occa- 



PLANT GEOGRAPHY. 



271 



sionalj periodical, or constant droughts. The various species of 
cactus are examples of drought plants. 

(3) Intermediate plants, or those which occupy a middle ground, 
requiring neither an excess of moisture nor of dryness. 

(4) Salt plants, or those whose existence depends not so much on 
the quantity of water present, as on the fact that this water contains 
certain saline or salty matters. 
Such plants are found on the 
shores of the ocean, or in the 
neighborhood of salt or alkaline 
springs. 

390. Distribution of Vege- 
tation. — The influence of heat 
and moisture is noticed as we 
pass from the equator to the 
poles, or from the base to the 
summit of a tropical mountain. 
Thus arise a horizontal and a 
vertical distribution of vegetation. 

The greatest luxuriance of 
vegetation is found in the equa- 
torial regions, where both heat 
and moisture are most abundant. 
Here a greater variety of species occurs, and the individual plants 
are large and brilliantly colored both in their leaves and flowers. 
As we pass toward the poles, the number of the species diminishes ; 
trees disappear, being replaced by shrubs and herbs, and these, in 
turn, by lichens and mosses, until, amid the snows of the polar lati- 
tudes, even the simplest forms of vegetable life are often wanting. 

391. There are various ways in which the vegetation of the earth 

may be studied : 

(1) According' to Meyen, we may divide the eartt's surface into zones ac- 
cording to the latitude, and the mountainous elevations into zones according to 
the altitude. Since the distribution of heat is not dependent on the latitude 
or the altitude alone, we may advantageously modify this plan, and divide the 
aones by the isotherms, as has been suggested by Dove. 




Fig. 122.— Sargassum. 



272 



PHYSICAL GEOQBAPHT. 



(2) According- to Schouw, we may divide the earth's surface into regions 
characterized by groups of peculiar floras, and separated by natural barriers. 

The great number of the regions required to give thoroughness to Schouw's 
system renders its use inadvisable. 

(3) According to Humboldt and others, we may divide the earth's surface 
into zones, according to the appearance of the plants inhabiting them. Here, 
plants of entirely different species are grouped by their mere outward resem- 
blances into what are called forms. 

The first method is the one most suitable for our purposes. We shall follow, in 
the main. Dove's modification, as adapted by A. E. Johnston, and divide the sur- 
face of the earth into zones, according to the isotherms or lines of mean annual tem- 

1 " ' rature. This system is based on the 
I ict that the character of the vegeta- 
lon is dependent mainly on the tem- 
perature, which, in its turn, regulates 
the quantity of moisture. 

392. Horizontal Zones of 
Vegetation. — The earth's hor- 
izontal zones of vegetation are 
as follows : 

(1) The Tropical Zone. 






Fig. 123.— Date Palm. 

(2) The Sub-tropical 
Zones. 

(3) The Warm Tem- 
perate Zones. 

(4) The Cold Tem- 
perate Zones. 

(5) The Sub-arctic Zone, or Zone of Conifers. 

(6) The Polar Zone, or Zone of Alpine shrubs, mosses, and lichena 



Fig. 124.— Avenue of Royal Palms, 



PLANT QEOOBAPHY. 



273 



393. The Tropical Zone, or the zone of palms, bananas, spices, 
and aromatic plants, lies on each side of the equator, between the 
isotherms of 73° Fahr. It includes most of the land within the 
tropics of both hemispheres. 

The excessive heat and moisture of this zone produce an especial 
luxuriance in the vegetation. Trees attain enormous size, the foliage 
is bright, the flowers brilliant, and the number of species great. The 
forests are characterized by a great variety of trees, and are almost 
impenetrable from the numerous parasitic plants with which the trees 
are covered, and the gigantic, rope-like climbers, or lianas, that twine 
among them. 

Palms, bananas, tree-lihe grasses, and orchids are among the charac- 
teristic plants. 

Orchids are curious plants, inhabiting damp forests. They attach themselves 
to trees and rocks, drawing nearly all their nourishment from the air. As a class, 
they are noted for their vivid coloring and the curious forms of their flowers. 
The well-known vanilla bean is obtained from an orchid. The grasses of tem- 
perate latitudes are repre- 
sented in the tropical zone 
by the bamboo, which often 
attains the height of 60 feet. 

The banyan-tree, a spe- 
cies of fig-tree, Fig. 125, is 
found in the East Indies. 
From a colossal trunk nu- 
merous air-branches are 
sent out, which, descending 
to the ground, take root, and 
in their turn send out other 
branches, and in this way 
an extended area is cov- 
ered. A single tree has 
been known sufliciently 
large to give shade to 7000 
men at the same time. Fig. 125.— Banyan-tree. 

The Llanos of the Orinoco lie in the tropical zone. During the 
dry season they are almost entirely devoid of vegetation ; but during 
the wet season they are covered with grasses. 

The Indian Archipelago affords an excellent illustration of the wonderful 
18 




274 rHYSICAL GEOGRAPHY. 

luxuriance of the vegetation of the tropics. Here the gigantic Eafllesia bears 
flowers three feet in diameter ! 

In the northern and southern portions of the tropical zone, where 
the mean annual temperature ranges from 79° to 73° Fahr., the 
vegetation, though similar to that of the equatorial regions, begins 
to lose its density and luxuriance. The forests contain less under- 
growth and fewer parasitic plants. Tree-like ferns and figs are 
especially abundant. 

394. The Sub-tropical Zones, or the Zones of Laurels and 
Myrtles, extend in each hemisphere, from the isotherm of 73° to 
68° Fahr. Here, the heat of summer, though sufficient to ripen 
most of the tropical fruits, is not so intense as in the tropical zone. 
The winters are mild, and scarcely arrest the vegetation. The palms 
and bananas of the preceding zones are common, but the charac- 
teristic vegetation is found in the abundance of trees with thick, shining 
leaves, such as the laurels, magnolias, and myrtles. 

395. The "Warm Temperate Zones, or the Zones of Ever- 
green Trees, or trees which do not shed their leaves, extend in each 
hemisphere, from the isotherm of 68° to 55° Fahr. In this zone, 
trees with thick, shining leaves occur, mingled with oaks, beeches, 
and others similar to those found in our own forests. No palms 
occur, but in their place we find a number of glossy-leaved, ever- 
green trees and handsome evergreen shrubs. 

In those portions of this zone which are in the neighborhood of the Mediter- 
ranean, the bay, myrtle, laurel, fig, and the olive are characteristic. The cork 
oaks, chestnuts, and pomegranates are frequent. The vine, said to be a native of 
this zone, attains here its greatest growth, the stem often reaching a thickness 
of half a foot. In America, oaks, pines, and tulip-trees occur. 

The southern warm temperate zone includes portions of New Zea- 
land and Australia, and in South America the Pampas of the Rio 
de la Plata, a region of grass-covered plains. 

396. The Cold Temperate Zone, or the Zone of Deciduous 
Trees, or those which drop their leaves in autumn, extends in the 
Northern Hemisphere, from the isotherm of 55° to 41° Fahr. For- 
ests of deciduous trees are the main characteristics of this zone ; oaks, 
birches, beeches, chestnuts, walnuts, maples, elms, larches, sycamores, 



PLANT QEOQBAPHY. 



275 



and alders are among the most common of the deciduous trees. 
Mosses and lichens frequently cover the trunks of the trees, and 
a rich and varied undergrowth occurs ; the holly, clematis, wild rose, 
honeysuckle, and rhododendron are examples. Extensive meadows, 
covered with grasses, are found in this zone. 

The deciduous character of the trees, and the almost total absence of ever- 
greens, produce a marked contrast between winter and summer. During winter, 
the foliage almost entirely disappears, and snow covers the ground for long 
periods. 

This zone is essentially one of extensive forests. In connection 

with the warm temper- 
,,. ate zone of the North- 

ern Hemisphere, it has 
always contained the most 
highly civilized races of 




Fig. 126. — Fir-trees, Yellow- 
stone Park. 

men, and is especially 
rich in the number and 
luxuriance of its food- 
plants. 

397. The Sub-arctic 
Zone, or the Zone of 
the Cone-bearing 
Trees, extends, in the 
Northern Hemisphere, from the isotherm of 41° Fahr.to regions where 
the mean annual temperature for the month of September is 36.5° 



Fig. 127.— The Pines, Byberry, Phila. 



276 PHYSICAL OEOGRAPHY. 

Fahr. In this zone both forests and grassy meadows abound. The 
forests are especially characterized by cone-bearing trees, with evergreen, 
shining, needle-shaped leaves, such as the pine, spruce, hemlock, cedar, 
and fir. In the northern portions of the zone beeches and alders 
are found, and willows, when the soil is moist. The meadows are 
covered with grasses and flowers, and afford abundant pasturage. 
The northern limit of trees is marked on the map of the plant regions. 

398. The Polar Zone, or the Zone of Alpine Shrubs, Mosses, 
Lichens, and Saxifrages, extends from the limits of the sub-arctic 
zone to the pole. In this zone no trees occur except those of a stunted 
growth. Alpine shrubs of tortuous, compact grow^th, such as the 
Alpine rhododendra, the dwarf birch, willow, and alder, occur. 
Sedges and grasses are found. The pastures of the preceding zones 
are absent; in their place we find extended areas covered with 
lichens. 

The northern plains of Siberia are covered with extensive marshes, called the 
Tundras, where the ground, during most of the year, is frozen to great depths. 
The short summers suffice to thaw the surface only, when a few mosses and 
lichens appear. 

Near the extreme northern limits of the polar zone, beyond the 
isotherm of 41° Fahr. for the month of July, such plants only are 
found as can thrive during the brief Arctic summer of from four to 
six weeks. Shrubs are entirely absent i lichens and mosses occur, 
together with stunted Alpine herbs. In Spitzbergen, lichens and 
mosses are found, the former being especially numerous. 

399. The Vertical Distribution of Vegetation.— It is difficult to make a 
satisfactory systematic distribution of vegetation into vertical zones, since the tem- 
perature and moisture, on which such an arrangement must be based, are subject 
to very considerable variations. Thus, the position of the mountain-ranges as 
regards the prevalent wind, the direction of the mountain slopes, and the extent 
cf the elevated plateaus, all exert so powerful an influence on the mean annual 
temperature and the rainfall, that in the same mountain-range, opposite slopes, 
or even different parts of the same slope, afford marked climatic contrasts. In 
ranges that are widely separated the differences are still greater. The following 
chart indicates the characteristic flora at similar elevations in the different 
continents. 



PLANT QEOQRAPHY. 



277 



(1) Between the level of the sea and. 5000 feet above the sea-level 
the vegetation is, in general, similar to that of the tropical and sub-tropical zones. 
Palms, bananas, tree-fei'us, barley, potatoes, sugar-cane, rice, and cotton are found 
in the lower parts. 

(2) Between 5000 and 10,000 feet, the vegetation is, in general, similar to 
that of the warm temperate zones. In America, the birch and cedar occur in the 




Fig. 128. — Vertical Distribution of Vegetation (Black). 



lower portions of the region, and Peruvian bark and the cinchona trees, so useful 
in medicine, in the upper portions. In Africa and Europe, the pine, birch, and 
oak occur ; and in Asia, the oak ; here also the vine is cultivated. 

(3) Between 10,000 and 15,000 feet, the vegetation, in general, is that 
of the cold temperate zones. Deciduous trees occur ; rye, wheat, barley, and oats 
are cultivated. 

(4) Between 15,000 and 20,000 feet, the flora corresponds, in general, to 
that of the polar and arctic zones. A few rhododendrons and birches occur on the 
warmer Asiatic slopes, and occasionally, crops of barley are cultivated. The 
greater part of this zone is covered with perpetual snow. 

In the descriptions here given, it will be noticed that the correspondence of 
the vertical and horizontal zones is but of a general character. 

40C^. Plant Regions. — In some localities a few plants occur in 
such vast numbers over extended areas as to give a characteristic 
appearance to the country they cover. A brief mention will be 
made of such regions, especially as they illustrate the influence of 
the presence or absence of moisture on the vegetation. 

401. Forests occur wherever the moisture is abundantly and 
regularly distributed throughout the year. As a rule, forests are 
limited to those portions of the world where the rain either falls at 



278 PHYSICAL GEOGRAPHY. 

all times of the year, or is abundant during the season in which the 
trees are growing, as in the zones of the prevailing westerly winds. 
Dense forests also occur in the tropics, where moisture is abundant, 
and some forms occur even in fairly arid districts. 
Forests may be divided into the following classes : 

(1) Evergreen Foliage Forests. — These occur mainly in the trop= 
ical regions, though they are sometimes found in the warmer parts 
of the temperate zones. They require excessive moisture and heat, 
and have been aptly styled " rainy forests." The soil is rich and 
black from the long accumulation of vegetable humus. Tree-ferns, 
palms, bamboos, with varied lianas or climbers, are characteristic. 
Aerial or parasitic plants find lodgement on the trees and climbers. 
These forests constitute the true " evergreen " trees ; the foliage is 
evergreen because ever-growing, leaves being almost constantly 
formed and shed. 

(2) Deciduous Forests, or those whose trees shed their leaves at 
regular periods. Such forests characterize the temperate zones. 
The leaves assume vivid coloring a short time before falling. In 
deciduous forests the undergrowth varies inversely with the thick- 
ness of the tree growth and the corresponding density of the shade. 
In beech forests the shade is so dense that the undergrowth is 
scanty. In oak forests the shade is not so dense, and the under- 
growth is more abundant. Deciduous forests are usually mixed, 
containing many varieties of trees, such as maple, oak, elm, beech, 
walnut, chestnut, hickory, etc. 

(3) Coniferous Forests are sometimes called evergreen forests. 
They are not evergreen because ever-growing, but because they do 
not shed all their narrow, needle-shaped leaves at one time as do the 
deciduous forests. Such forests include among other trees the pine, 
spruce, cedar, fir, and hemlock. Where the forests consist mainly of 
pines, the shade is not so dense as those in which the fir or hemlock 
prevails. These trees are capable of existing with a comparatively 
limited watei'-supply, the small surface of the needle-shaped leaves 
with thick walls preventing excessive loss of water. 

(4) Leafless Forests are characteristic of such tropical regions as 



gitude 40 West from 20 Greenwich Longitude 20 East from 40 Greenwich GO 




PLANT GEOGRAPHY. 279 

Java and the arid lands lying near the Gulf of California, both in 
the United States and Mexico. Here the soil is bare and dry, 
and the trees possess no leaves. In some regions, for example, 
near the Gulf of California, varieties of the great cactus repre- 
sent the tree forms of vegetation. 

(5) Swamp Forests include willows, alders, birches, etc. Conifers, 
such as hemlocks, pines, junipers, cypress, and the larch, also occur. 

402. Steppes. — When the moisture is scanty and not weU 
distributed throughout the year, but the rainfall is periodical, 
and long droughts occur in the intervals between the rainy seasons, 
the forests are replaced by areas called steppes, which, during the 
wet seasons, are covered with grasses, shrubs, or herbs ; but during 
the dry seasons are almost destitute of vegetation. Steppes are 
found in the Llanos and Pampas of South America, in the Great 
Plains of North America, in the grassy steppes of Australia, Russia, 
and Asia, in the German heaths, and in the African savannas. 

Salt steppes, which sometimes occur, are characterized by the 
absence of vegetation, caused not so much by absence of moisture 
as by the presence of saline substances. The steppe of the Great 
Salt Lake region in the United States form-s an example. As we 
have already seen, all such regions are characterized by a limited 
water-supply. 

403. Meadows and Prairies. — Meadows and prairies, like 
steppes, are covered with tall grasses, but the vegetation is more 
permanent, the droughts being only occasional. They are found, 
therefore, in the temperate zones, in the regions of constant rains. 
An extended prairie region is found in the valley of the Missis- 
sippi, on both sides of the stream. 

404. Deserts are regions characterized by an almost entire 
absence of vegetation ; they are found mainly in the zones of the 
trade winds, and are to be ascribed entirely to the absence of moist- 
ure. Their bare surfaces are subject to great and sudden changes 
of temperature, being, as a rule, excessively warm during the day, 
and often quite cool at night. These changes are due to the readi- 
ness with which a bare surface receives and parts with heat. 



280 PHYSICAL GEOGRAPHY. 

Deserts occur, however, in parts of the world outside the zonea 
of the trade winds, and may be divided into the following classes : 

(1) Tropical Deserts. — Here the water-supply is a minimum and 
the heat a maximum, vegetation is almost entirely absent, and the 
soil is bare. 

(2) Cactus Deserts. — Such deserts are characteristic of parts of 
the South-western United States, including Texas, New Mexico, Ari- 
zona, and Southern California. The spines, bristles, and thorny 
walls of these plants protect them from attacks of animals. 

(3) Salt and Alkaline Deserts. — These are due to the presence 



'^m 



S?ig. 129.— American Beeei-S. 

of large quantities of alkali in the soil. Death Valley in Southern 
California and the region in the neighborhood of the Dead Sea in 
Arabia are examples. 

405. Swamp Moors are meadow-like stretches of swampy ground. 
They occur especially on the borders of reed swamps, on the side 
nearer the land. They are characterized by sedges and coarse 
grasses. In some cases trees and shrubs, such as alders, willows, 
and birches, flourish, thus making a swamp thicket. 

406. Sphagnum Moors, so called from the almost exclusive 
occurrence of the common peat or bog moss called the sphagnum. 



PLANT GEOGRAPHY. 281 

These mosses continue their upward growth after the lower parts 
have died. They grow rapidly, and make such inroads on the 
waters of shallow lakes as to transform the lake into a marsh or 
qucking bog. 

A peculiarity of such moors is found in the antiseptic character 
of their water, which prevents the growth of those plant forms 
known as bacteria, which aid in producing decay. For this reason 
the bodies of animals submerged in such water do not decay. 



CHAPTER II. 

Cultivated Plants. 

407. Plants appear to have been originally confined, by condi- 
tions of soil or climate, to certain localities, from which they have 
gradually spread to other localities where conditions exist favorable 
to their growth. In many instances, however, plants furnishing 
materials for food, clothing, or other staples for the human family, 
have been purposely transplanted and widely diffused by man. 
In these cases their successful cultivation is limited to regions where 
suitable climate and soil either existed naturally, or have been arti- 
ficially produced. 

408. Distribution of the Cereals. — The cereals include barley, 
rye, oats, wheat, maize or Indian corn, and buckwheat. The cereals 
and the potato form the most important food-plants of the temperate 
zones. 

Barley, thought to be a native of Tartary, can be grown farther 
north than any other grain ; it is found in Lapland, as far as 70" 
N. Lat. ; it is largely used in brewing malt liquors. 

Rye is round in Norway as far north as Lat. 67° N. It is the 
most common grain in Russia, Germany, and in portions of France. 

Oats iL, probably, a native of the Caucasus ; its northern limit is 
about 65° N. Lat. in Norway. 

Wheat is, probably, a native of Tartary. It is the most impor- 
tant of the cereals, and has a wide vertical and horizontal distribu- 



282 



PHYSICAL GEOGRAPHY. 



tion. Its northern limit is 64° IST. Lat. in Norway. It is the food 
grain of nearly all the civilized nations of the earth. The northern 
states of the United States, and the southern parts of Canada, are 
the principal producers. Russia is also a large producer. 

Maize, or Indian Corn, a native of America, is extensively cul- 
tivated from the southern part of 
Chili to high latitudes in North 
America. It forms one of the most 
valuable food crops in the United 
States. Its northern European 
[ 'v W^5r^^5^^^\\l I 11// // ^ limit is, perhaps, near the iso- 
therm of 65° Fahr. 

Buckwheat, a native of the 

\ >JW \ ViyV^Cj^flf //' I // colder portions of the Chinese 

-'f/MH ^IllcU^^S / / / \ Empire, is extensively cultivated 

^\^\\V ^^^ v^^^^W / / / ^^ ^^^® plateaus of Central Asia, 

and, generally, in the cool temper- 
ate regions of the rest of the 
world. Buckwheat is especially 
valuable on account of the ability 
it possesses of thriving in sandy 
or moory soils, where other simi- 
lar food-plants will not succeed. 
Potatoes. — The native country 
of this important food product appears to have been either Chili or 
Peru. Though cultivated in both the tropical and temperate regions, 
it is to be regarded as a food-plant of the temperate zones. It pos- 
sesses a very remarkable range, being cultivated from the extremity 
of Africa to Lapland : the requisite temperature for its culture in the 
tropical regions being found on mountain-slopes. 

409. The Food-plants of the Tropical Regions are rice, dates, 
cocoanuts, bananas and 'plantains, cassava.^ bread-fruit, sago, yams, etc. 

Rice is the seed of a variety of grass that grows in tropical swamp 
lands. It is a native of China. It is cultivated in China, Central 
America, Africa, Egypt, Nubia, Persia, the Americas, and the West 




Fig. 130. — Maize, or Indian Corn. 



CULTIVATED PLANTS. 



283 



Indies. It requires considerable heat and an abundance of moisture. 
Rice forms the main food of a large proportion of the world's popu- 
lation. 

Dates form an important article of food in North Africa, both for 
man and beast. Dates are obtained from the date-palm, a native of 
a strip of land on the southern slopes of the Atlas Mountains, where 
the tree occurs so plentifully as to give to the country the name of 
Beled-el-Jerid, or the Land of Dates. Different varieties of the 
date are found in the Saharan oases and in other parts of the world. 

Cocoanuts are the product of the cocoa-palm, which is valuable 
for its food, timber, foliage, and fibres. The cocoa-palm is a native 
of Southern Asia, but 
is cultivated throughout 
the tropical regions of 
Ceylon, Sumatra, Java, 
and the islands of Poly- 
nesia. 

Bananas and Plan- 
tains are thought to 
be natives of Southern 
Asia. They are ex- 
tensively cultivated 
throughout the tropical 
zones, both north and 
south of the equator. 
Since their fruit is very 
nutritious, and the yield 
of a given area great, 
they form an exceed- 
ingly important staple 
of food. 

Cassava, a nutritive, 
starchy material, is obtained from the root of the manioc, a tropical 
shrub. In some species the fleshy root is several feet long, and is 
nearly as thick as a man's arm. Cassava meal is obtained by 




Banana-tree. 



284 



PHYSICAL GEOGBAPHY, 



pounding or beating the root and heating it, in order to expel a 
poisonous principle which it contains. Tapioca is prepared from 
cassava. The manioc is a native of Brazil, but is cultivated in 
Western Africa, in Congo, and in Guinea. 

Bread-fruit is the pulpy fruit of a tree which grows only in the 
tropics. The fruit, when baked, resembles bread in taste. The tree 

yields fruit during 
most of the year; 
it is said to be a 
^^ native of the South 

Sea Islands, though 
it is now quite com- 
~^\ men in the Friend- 
ly and Society 
I groups,andinmany 
of the neighboring 
^1 islands. 
I I Sago is a starchy 

substance, obtained 
from the pith of 
several species of 
palm trees which 
grow in the Moluc- 
cas. A single tree 
often yields from 600 to 800 pounds of sago. 

Yarus are the large tubers of a number of plants resembling 
sweet potatoes. They are cultivated in the Southern United States, 
in Africa, in South America, and in the West Indies. 

410. Sugar-cane is a native of India, but is now extensively 
cultivated throughout the tropical and warm temperate zones of 
both hemispheres, in the West Indies, Southern United States, 
Guinea, Brazil, Mauritius, Bourbon, Bengal, Siam, China, Java, 
and the neighboring islands. 

Beets are cultivt'ted in large quantities in Europe and in Cali- 
fornia for the production of sugar. 




Fig. 132.— Bread-fruit. 



CULTIVATED PLANTS. 



285 



411. Fruits of the Tropical and Warm Temperate Zones. — 

Besides those already enumerated, we find the following : oranges, 
lemons, limes, citrons, pineapples, mangoes, Jigs ; 
and, in the cooler portions, cherries, peaches, apri- 
cots, and pomegranates. 

412. Distribution of Plants yielding Bev- 
erages, — The principal plants yielding bever- 
ages by infusion are tea, coffee, and cocoa. 

Tea consists of the dried leaves of a number 
of evergreen shrubs, natives oi' China. Tea is 
cultivated in China, Japan, and Assam, the 
principal tea-producing countries of the world. 
It is cultivated also in Java, Southern India, 
Ceylon, Australia, Natal, and Brazil. Tea is 
cultivated in Japan as far as Lat. 39° N. Tea 
was introduced into Europe by the Dutch, in 
1610. 

Coffee is the berry of a tree found native in 
Abyssinia. The tree attains a height of from 
15 to 20 feet ; it has shining green leaves, 
and bears white flowers, which are followed by 
reddish-brown berries, each of which contains 
two grains of coffee. Brazil is the greatest 
coffee-producing country of the world. Coffee 
is grown also in the northern and north-western 
parts of South America, in the West Indies, in 
Java, Sumatra, Ceylon, Mauritius, Southern 
Arabia, and on the west coast of Africa. 

Cocoa. — The cocoa-tree is cultivated in Cen- 
tral America, Guiana, Chili, India, Japan, and 
in several islands in the Indian Ocean. The tree attains a height of 
about 20 feet. Chocolate is prepared from the seed of the cocoa-tree. 

413. Spices, such as pepper, cloves, nutmeg, and cinnamon, are cul- 
tivated mainly within the tropics. Vanilla, used in flavoring, is 
limited to this region. 




Fig. 133.— Sugar- 
cane. 



286 



PHYSICAL GEOGRAPHY. 



Pepper. — Black pepper is the dried seed of a climbing shrub that 
grows wild in Western Hindostan. It is raised in the West Indies, 
in Siam, in the Philippines, and in the Malay Peninsula. Red or 
Cayenne pepper is grown in Guiana and the East. 

Cloves are the dried flower-buds of an evergreen tree, a native of 
the Moluccas. It is grown extensively in the island of Amboyna, 
in the Malay Archipelago, in Zanzibar, in Guiana, and in the West 
Indies. 





Fig. 134.— Tea-plant. 



Fig. 135.— Coffee. 



Nutmegs are the seed of a tree that grows in the Banda Islands 
and in the Moluccas. The tree is now grown in tropical America, in 
Mauritius, and in Madagascar The nutmeg is covered by several 
layers of vegetable matter, one of which is the mace of commerce. 

Cinnamon is the inner bark of a small tree growing wild in 
Ceylon. It is cultivated in Ceylon and many other tropical countries. 

Vanilla is obtained from the dried, fragrant pods of a plant grown 
mainly in Mexico, Central America, and Brazil. 

414. The Principal Narcotics used in different parts of the 
world are opium, prepared from a species of poppy ; the betel-plant, 
a native of Hindostan, the leaves of which are chewed, together 



CULTIVATED PLANTS. 287 

with the areca-nut ; hasheesh, a narcotic used in India ; and tobacco, 
the dried leaves of a plant grown extensively in Mexico, Cuba, 
Brazil, and in the United States. 

415. Plants Valuable for giving' Materials for Clothing are 
cotton, hemp, and flax. 

Cotton is a native of India. The principal cotton-fields of the 
world are in the Southern United States, India, China, Africa, 
Egypt, Australia, Southern Europe, South America, and the West 
Indies. Cotton is among the most valuable of the vegetable sta- 
ples. Its culture and manufacture give employment to many 
people, and have been an important factor in the development of 
the human race. 

Hemp and Flax are cultivated in the temperate regions of Rus- 
sia and throughout Great Britain and the United States. The 
Philippine Islands produce an especially valuable variety. 

The plants producing medicines, and products employed in the 
arts or manufactures, are : 

The Cinchona-tree, found on the upper slopes of the tropical 
Andes. Quinine is obtained from the bark of the tree. 

Gum Arabic, obtained from the East Indies, Egypt, and Africa. 

Indigo, a blue dye, obtained from the indigo-bearing plants. 

Brazil-wood, Nicaragua-wood, and Log--v70od yield reddish 
dyes. 

Qnercitron and Black Oak yield a yellow dye. 

Turpentine and Rosin are products of the pine tree. 

Caoutchouc, or India-rubber, is the juice of a tropical tree. 

Olive Oil is derived from the fruit of the olive-tree, cultivated 
on the borders of the Mediterranean. 

Cocoanut, Palm, Flaxseed, and Cotton-seed Oils are ob« 
tained respectively from the cocoanut, the palm, and the seeds of 
flax and cotton. 



oJ»Jc 



288 PHYSICAL OEOQEAPHY. 

SYLLABUS. 

Only plants containing chlorophyll can prepare their own food directly from 
materials taken from the soil or from the air. Such plants, by photosynthesis, 
change carbon dioxide and water into carbohydrates and give olf oxygen. 

Plant geography treats of the distribution of plants. It differs from botany, 
which treats of the structure of plants. 

The plants of any section of country, taken collectively, are called its flora. 

Plants require for their vigorous growth certain conditions of light, heat, 
moisture, and soil; of these, moisture, heat, and light are the most important. 

Plants may be divided into societies of water plants, drought plants, plants 
intermediate between water and drought plants, and salt plants. 

The distribution of heat and moisture forms the true basis for the distribution 
of plant life. 

The surface of the earth is divided into the following horizontal zones of vege- 
tation : tropical, sub-tropical, warm temperate, cold temperate, sub-arctic, and 
polar. 

The tropical zone is characterized by the prevalence of palms, bananas, spices, 
and aromatic plants. 

The sub-tropical zones are characterized by the prevalence of laurels, myrtles, 
and magnolias. 

The warm temperate zones are characterized by forests of evergreen trees ; 
the cold temperate zones by forests of deciduous trees. Oaks, birches, beeches, 
chestnuts, walnuts, maples, elms, larches, alders, and sycamores are among the 
most common of the deciduous trees of the temperate zones. 

The sub-arctic zone is characterized by cone-bearing trees. 

The polar zone, by Alpine shrubs and mosses. 

SteppQs are plains of the cold temperate and sub-arctic zones characterized by 
a scanty vegetation of grasses and low shrubs. 

Forests require for their luxuriant growth an abundance of moisture, fairly 
distributed either throughout the year, or during the time the trees are growing. 

Forests may be divided into: (1) Evergreen foliage forests; (2) Deciduous for- 
ests ; (3) Coniferous forests ; (4) Leafless forests ; (5) Swamp forests. 

Deserts may be divided into: (1) Tropical deserts ; (2) Cactus deserts; (3) Salt 
and Alkaline deserts. 

The principal cereals are barley, rye, oats, wheat, maize or corn, and buck- 
wheat. 

The principal food-plants of the tropical regions are rice, dates, cocoanuts, 
bananas, plantains, cassava, bread-fruit, sago, yams, etc. 

Some of the most important plants cultivated for the beverages they yield are 
tea, coffee, and cocoa. 

The principal spices are pepper, cloves, nutmegs, and cinnamon. The princi- 
pal narcotics are opium, betel, hasheesh, and tobacco. 

Cotton, hemp, and flax are valuable for furnishing materials for clothing. 



I 



SYLLABUS. 289 

REVIEW QUESTIONS, 

Why are animals dependent upon plants for their existence ? 

Define photosynthesis. Describe the formation of soil. Why is soil of com- 
paratively less importance to the existence of vegetation than heat or moisture ? 
Name the conditions requisite for plant growth. 

Enumerate some well-marked plant societies. 

What do you understand by the horizontal distribution of vegetation? By 
the vertical distribution ? 

Why should the isothermal lines form the boundaries of the plant zones? 

Name the horizontal zones of vegetation. State the boundaries of each. 

What is the characteristic flora of the tropical zone ? 

How do the forests of the cold temperate zones diifer from those of other zones? 

Into what different classes may forests be divided ? 

By what climatic conditions are steppes produced? 

What conditions are requisite for the production of meadows and prairies? 

How are deserts produced 9 

Into what different classes may deserts be divided ? 

Name some of the more important cereals. 

Name the principal food-plants of the tropical regions. 

Name some of the fruits of the tropical and warm temperate zones. 

In what portions of the world is coffee successfully cultivated? Where is tea 
cultivated? From what tree is chocolate obtained? From what tree are cloves 
obtained? Where is the tree cultivated?- Where are nutmegs grown? What 
is mace? In what part of the world is cinnamon cultivated? 

Name the plants which furnish materials for clothing. 



o>»ic 



MAP QUESTIONS, 

Name some parts of the world included in the tropical zone of vegetation. 

Name the plants of the tropical zone which are characteristic of South Amer- 
ica. Name those of Africa. Of India and Australia. 

Describe the principal region of the cocoanut palm, bread-fruit, sago, and yam 
in the Eastern Continent. 

Describe from the map the limits of the sub-tropical plant zones. Describe the 
characteristic flora of those portions of each of the continents which lie within 
these zones. 

Describe the limits of the warm temperate plant zones. Of the cold tem> 
perate plant zones. Of the sub-arctic zone. Of the polar zone. 

Trace on the map the northern limit of trees. The southern limit. 

Name some of the trees of the warm temperate zones. Of the cold temp6ratifc 
zones. Of the sub-arctic zones. 

19 



290 PHYSICAL QEOQBAPHT. 

SECTION II. 

ANIMAL LIFE. 

CHAPTER I. 

Zoological Geography. 

416. Zoological Geography, or, as it is sometimes called, Zoo- 
geography, treats of the distribution of animal life. The animals 
found in any region of country are called its fauna. Like plants, 
animal species appear to have originated in certain localities, 
from which they have spread, more or less widely, over adjoining 
areas. 

Since animals derive their food, either directly or indirectly, from 
plants, animal life is necessarily dependent on plant life for its ex- 
istence. Though able to move freely from place to place, animals 
are, nevertheless, restricted by conditions of food and climate to 
fairly well-defined areas, which are not, however, so sharply defined 
as in the case of plants. 

When the proper conditions of food and moisture are present in 
any region, its animals multiply so rapidly that the region can no 
longer produce a sufficient food-supply for them, so that some of 
them must either perish or seek a new home. 

417. Dispersal. — A dispersal, therefore, begins, the animals 
gradually invading regions adjoining their original homes. Dis- 
persal, however, is not alone due to lack of food-supply. Many 
causes unite to efiect dispersal and distribution of animal life ; for 
example, animals are carried from one place to another by winds, or 
by ocean or river currents ; or they are accidentally carried by 
some of the means employed by commerce for transporting commodi- 
ties from one region to another ; or they are carried to considerable 
distances by means of other animals, thus, the eggs of certain 
fresh-water mollusks ofken adhere to the feet of aquatic birds, and 



ZOOLOGICAL GEOGRAPHY. 291 

80 are transported to distant countries; or they are purposely 
carried by man from one region to another. 

418. Barriers. — This dispersal is, however, not unopposed. There 
are various obstacles or harriers that oppose the unrestricted dis- 
persal or migration of animal life. These barriers are physiographic, 
or those which exist outside the animal, and physiological, or those 
which exist within the animal. 

The principal physiographic harriers are large hodies of water, such 
as the ocean, arms of the sea, rivers, extensive and elevated mountain- 
ranges, deserts, and forests. 

The physiological or climatic harriers are either heat harriers, 
indicated by the isothermal lines, or food harriers, which arise from 
]ack of suitable food. They depend on conditions or peculiarities 
of structure existing within the animal, arising from the limits of 
temperature beyond which the animal cannot live, and the character 
of the food it requires for its continued existence. 

419. Physiographic Barriers. — Probably the most effective of 
the physiographic barriers are large bodies of water. When very 
large, these are practically insurmountable. For this reason the 
fauna of islands usually differs widely from that of the adjoining 
mainland ; for example, the island of Madagascar possesses a fauna 
so distinct from the neighboring coasts of Africa that some authori- 
ties place it in a separate animal region. Again, the Gallapagos 
Islands, situated some 600 miles west of Ecuador, have a fauna 
distinctly different from that of the mainland. 

During periods of river floods, such as those which occur in many tropical 
regions, water barriers are sometimes surmounted by huge floating rafts formed 
by the accumulations of forest trees bound together by various creeping or climb- 
ing plants. These rafts, aflbrding temporary shelter to numerous and varied 
types of animal life, have been seen near the mouths of large rivers, such as the 
Amazon, the Ganges, and the Mississippi. Being carried to sea, they may readily, 
through the agency of the winds or ocean currents, transport certain animal 
species to distant, and otherwise inaccessible, islands or continents. 

Extensive and elevated mountain-ranges offer a serious barrier to 
the migration of most forms of animal life. This arises not only 
from the animal's limited powers of locomotion and the different 



292 PHYSICAL OEOGRAPHY. 

conditions of air-pressure, temperature, and moisture existing in tli« 
higher regions of the atmosphere, but also from the difference in the 
climate of the opposite slopes. Even, therefore, if the animals were 
transported to the opposite slopes, they might not be able to con" 
tinue to live under the new conditions there existing. It is for this 
reason that the fauna of opposite mountain slopes often vary. 

Deserts offer an insurmountable barrier to those forms of animal 
life that require a moist climate. Forests may serve as a barrier 
to forms of life that ordinarily live on the prairies or in the open 
country. 

4:20. Physiological Barriers, or those existing within the ani- 
mals, are those which, by reason of the animal's physiological 
peculiarities, restrict it to certain varieties of food and to certain 
climatic conditions for its home or habitat. In other words, the 
existence of the animal is dependent on the character of its environ- 
ment. Every species of animal demands, for its continued existence, 
certain conditions of food, heat, light, and moisture. In some cases 
these conditions are so wide in range that the animals are able to 
exist over an extended territory. In other cases they are more 
limited, and the range of the animal is correspondingly restricted. 
An example of the effect of a climatic barrier is to be found in the 
difference in some of the fauna of the north temperate and arctic 
regions, and the south temperate and antarctic regions. Here, 
although the climatic conditions are practically the same, yet the 
climatic barrier of the intervening tropical zone is too great to per- 
mit of their intermingling. 

421. Acclimation. — Many animals possess the power of becom- 
ing acclimated, or being able to live in an environment differing 
widely from that in which the species originated. 

Animals differ greatly in this respect. Some species possess an 
exceedingly wide range, like the African elephant, which extends over 
the entire continent south of the Sahara. The tiger, too, is found 
over all of Central and Southern Asia from the east to the west. 
The American panther or cougar has a still greater range, extend- 
ing from Canada, on the extreme north, to Patagonia, on the south, 




Longitude 140 East from 160 Greenwich 



120 Longitude 100 West 80 frol 




»NTARCT C CIRCLE 



REFERENCES 

I AUSTRALIAN REGION I 1 

Ineotropicai " I I 
Inearctic " K^^ 



ETHIOPIAN REGION 
PALEARCTIC ■■ 
ORIENTAL 







E 



A 



N 



longitude 20 East from 40 Greenwicli 



ZOOLOGICAL GEOGRAPHY. 



293 



But with other species the power of acclimation is more limited. 
In the case of some animals the extent of their habitat is exceed- 
ingly restricted. For example, the buschbok, a species of antelope, 
is found only in the neighborhood of Port Natal, in South Africa. 
The red bird of paradise is found only within the narrow limits 
of a small island north-west of New Guinea. A beautiful species 
of humming bird has been found only near the summit of Chim- 
borazo, a volcanic mountain in equatorial South America. 

422, Heredity and Variation. — There are certain peculiarities 
of growth and development of animal life that exercise signal influ- 
ence in determining the ease with which a given animal may become 
acclimated. These are the principles of heredity and variation. 
An animal resembles its parents or ancestors. Although slight 
variations from the original type may sometimes occur, yet the 
tendency to revert to this original type always exists, so that an 
animal, even after many generations, more or less closely resem- 
bles its remote ancestors. When an animal wanders into a region 
where its environment varies from that in which it was born, if 
nnable to adapt itself readily and. entirely to the changes in en- 
vironment, it either ceases to exist, or, if the 
changes are not too great, it gradually adapts 
itself to the new conditions, ultimately devel- 
oping marked departures from its original type. 
If, therefore, the time during which these de- 
partures are occurring is sufficiently prolonged, 
the remote descendant may fail to possess the 
peculiarities of its ancestors, and a new species 
may thus result. For example, a bird obliged 
to obtain its food from the water may become a 
wader or a swimmer ; in some cases, as in the 
penguin, it has but rudimentary wings ; and so 
with other species. In such cases these newly 
developed species would be unable to live if suddenly transported to 
their original habitat. 

423. Survival of the Fittest. — But when an animal has 




Fig. 136.— Penguin, 



294 PHYSICAL GEOGRAPHY. 

reached a distant region, even if the climatic and food condi- 
tions are favorable to its continued existence, it may have to meet 
another condition before it can continue to exist in the new local- 
ity. The transported animal may find the new region already fully 
occupied by other animals, either its natural enemies, preying upon 
it, or its natural rivals, competing with it for the same food-supply, 
so that it must either exterminate, or drive them out, or be extermi- 
nated, or driven out, by them. Thus begins a struggle for existence 
which almost invariably terminates with the survival of the fittest ; 
i. e., that animal which can best adapt itself to the requirements of 
the environment, finally possesses the country. It is during this 
struggle for existence that variations or departures from the orig- 
inal type are apt to occur. These variations ultimately result in the 
production of species difiering in many respects from the original 
type. 

Sometimes animals purposely introduced into a new country find the condi- 
tions so favorable to their continued existence, or acquire variations that so 
well fit them to the conditions of the new environment, that they rapidly 
multiply, and at times even drive out or exterminate the native species. Exam- 
ples of this are found in the rabbits and pigs in Australia that now run wild in 
that country ; in the common brown rat brought here from Norway, that has 
driven out our indigenous black rat ; in the rapid multiplication of horses and 
cattle in South America ; in the extremely rapid multiplication of the English 
sparrow in the United States ; and in the successful introduction of various 
food fishes into waters far distant from those to which they are indigenous. 
For example, the shad, a fish native to the Atlantic coast waters and rivers of 
the United States, has been successfully introduced into the Pacific coast waters 
and rivers, and is now abundant there. The carp, a foreign fish, is rapidly 
becoming a nuisance in our waters, threatening the extermination of more 
valuable food fish by devouring their spawn. 

424. Distribution of Animal Life. — We distinguish a horizoyi- 
tal and a vertical distribution of animal life. 

As a rule, the luxuriance and density of terrestrial animal life 
decrease as we pass from the equator to the poles. The abundant 
heat and moisture of the tropics produce a vigorous vegetation, and, 
as a rule, all forms of terrestrial animal life, except man, there attain 
their greatest development both in size and activity. There are, 



ZOOLOGICAL QEOOBAPHY. 



295 



however, districts where the development of vegetation is so great 
that the luxuriance and variety of some types of animal life are 
noticeably decreased. As we proceed toward the poles the species 
are less developed, although in the temperate regions large and 
vigorous animals are still numerous. In the polar zones life is 
still less developed, although the reindeer and white bear are large, 
powerful animals. 

425. Vertical Distribution of Life. — In passing from the base 
to the summit of a high tropical mountain something of the same 
change is noticed in the species of animals as in passing along the 
surface of the earth from the equator to the poles. 

Fig. 137, indicates the characteristic fauna at similar elevations 



AMERICA 




Fig. 137.— Vertical Distribution of Animal Life (after Black). 



on the different continents. The arrangement is but an approxi. 
mation, yet, in general, animals found on the slopes of tropical 
mountains, at elevations between the sea-level and 5000 to 7000 
feet, correspond to those inhabiting the physical tropical zone; 
while those between 5000 or 7000 to 15,000 feet more nearly 
resemble those of the physical temperate zone. Birds of prey 
have exceptional vertical range. The condor, a great tropical vul- 
ture, is found in the high Andes far above the snow-line, overtop- 
ping in its flight the loftiest peaks. 

The fauna of neighboring mountain-ranges is often very dif- 
ferent. A particular species at a given elevation on one range 



296 PHYSICAL GEOGRAPHY. 

is frequently eotirely wanting on a neighboring, disconnected range, 
even though the same conditions of heat, moisture, and vegetation 
exist. The temperature of the intervening lower country, through 
which the animal would have to pass in order to reach the adjoining 
slopes, apparently forms an impenetrable barrier. 

426. Realms or Regions of Animal Life. — While, however, 
the isothermal lines, which govern the distribution of heat, moisture,, 
and vegetation, form a basis for the distribution of animal life, yet 
they cannot be taken as the actual boundaries of the animal regions, 
as they do not take into account the variations produced in species 
by the various natural barriers that have opposed their free 
dispersal. 

That climatic conditions and food-supply, which are dependent 
on climate, act as barriers to limit the dispersal of certain animals, 
there can be no doubt ; but they do not, in all cases, constitute the 
determining factors, because the ability of the animal to become 
acclimated may enable it to continue to exist under an environ- 
ment differing widely from that of its original home. 

Any portions of the world that have been long isolated from 
adjoining portions by efficient barriers will have peculiar, char- 
acteristic fauna, while portions devoid of such barriers will, in 
most cases, fail to possess any marked faunal peculiarities. Conse- 
quently, gradual elevations and subsidences, by isolating certain 
areas of land, or by bringing formerly isolated areas into contact 
with neighboring land masses, by producing changes in the loca- 
tion of mountain-ranges, deserts, forest regions, or other physical 
features, have been attended by marked changes in the fauna that 
exists in the changed region and its environs. 

As regards animal realms or regions, we may conclude, as has 
been pointed out by Jordan and Kelley, that in whatever parts 
of the earth conditions exist suitable for the growth of certain 
species of animals, such animals will be found there, unless — 

(1) Insurmountable barriers oppose them ; or, 

(2) Having reached the new region, they are unable to continue 
their existence from inability to adapt themselves to the conditions 



ZOOLOGICAL QEOGBAPHY. 297 

of the new environment, or, in the struggle for existence, to oppose 
successfully the animals already occupying the region ; or, 

(3) They have adapted themselves so well to the new conditions 
as to become distinct species that can only with difficulty be traced 
to their original stock. 

427. Animal Realms or Regions. — The following realms of 
animal life are based on Wallace's adaptation of Sclater's Realms : 

(1) The Nearctic Region, including all of North America except 
Central America, Mexico, and the Antilles. Its exact southern 
boundaries are somewhat in dispute, Arizona, New Mexico, and 
parts of adjoining States being by some authorities included in the 
Neotropic region. 

(2) The Neotropic Region, including all of South America, to- 
gether with Central America, the lowlands of Mexico, and the 
Antilles. 

(3) The Palcearctic Region, including all of Europe and Asia, 
excepting the tropical and sub-tropical parts, from Iceland to Bering 
Strait, and from the Azores Islands to Japan. It includes Africa 
north of the Tropic of Cancer, northern Arabia, all of Persia, 
Afghanistan, Beloochistan to the Indus, Thibet, Mongolia, and part 
of China. The Himalayas form part of its southern boundary. 

(4) The Ethiopian Region, including all of Africa and Arabia 
not embraced in the preceding regions, and the island of Mada- 
gascar. 

(5) The Oriental Region, including all of India and China from 
the limits of the preceding region to and inclusive of the Malay 
peninsula. It includes also the islands of the Malay Archipelago 
eastward to the island of Bali, together with Borneo, the Philippine 
Islands, and Formosa. 

(6) The Australian Region, including the continent of Australia, 
the islands of the Malay Archipelago east of Bali, together with 
Lombok, Celebes, Papua or New Guinea, New Zealand, and the 
tropical islands of the Pacific. 

Each of these regions is divided into a number of sub-regions 
whose names and boundaries are marked on the map. 



298 PHYSICAL GEOGRAPHY. 

428. Influence of Geographic Peculiarities on the Animal 
Reg-ions. — The animal regions enumerated are clearly determined 
by the geographic features. 

Thus, North America is nearly separated from South America; 
hence the peculiar fauna of each continent. Still this separation is 
not complete ; the isthmus of Panama is well watered and covered 
by luxuriant vegetation ; hence some species wander over the 
entire Western Continent from the Arctic Ocean to Patagonia. 

Europe and Asia form a single land mass (Eurasia) and have no 
effective barrier between them, the Ural Mountains not forming a 
continuous sepatating wall ; hence the two have largely the same 
fauna, and are included in a single region. 

Africa is separated from Europe and Asia by the Mediterranean 
Sea. The narrow isthmus of Suez is practically a desert. More- 
over, the Sahara forms an effective barrier ; hence the peculiar fauna 
of the two countries. Besides this, geological evidence shows that 
the sea covered part of the Sahara at a comparatively recent period. 

The Himalayas act as a barrier between Hindostan on the south, 
and the portion of Asia on the north ; hence the difference in their 
fauna. 

Australia is separated from Asia by numerous island chains; 
hence its characteristic fauna. 

The northern continents were elevated during the period of 
the glacial epoch, and a notable decrease of temperature occurred 
which profoundly altered the distribution and forms of life that 
existed during the warmer climate that prevailed prior to this 
epoch. 

It is not surprising, therefore, that, in many instances, difficulties 
exist in satisfactorily arranging animals in distinct regions or realms, 
considering the great extent of time during which animal life has 
existed on the earth, and the many and various changes that have 
occurred in the conditions of its environment. 

429. The Nearctic Region. — This region, extending as it does 
from the Arctic Archipelago and the extreme north of Greenland 
to tropical Mexico, possesses every variety of climate, from that of 



ZOOLOGICAL GEOQBAPHY. 



299 



the arctic zone to that of the tropics. Its vast mountain-system 
extending from north to south, with wide, interlying valleys, does 
not offer barriers so effective as if it crossed the continent from the 
Atlantic to the Pacific. Many species of animals roam, therefore, 
throughout the entire region. 

Among the characteristic animals of the Nearctic Region are the 
wolf, the fox, the formidable grizzly bear, the polar bear, the black 
bear, the lynx, the cougar or American panther, whose habitat em- 
braces the wide range of nearly the entire Western Continent ; the 
musk ox, the bison, now practically extinct, the moose, the cari- 
bou, the elk, several species of deer, the Rocky Mountain sheep 
and goat, the antelope, the raccoon, the Canada porcupine, numer- 
ous fur-bearing animals, such as the beaver and otter, and many 
rodents, such as prairie-dogs, rats, gophers, squirrels, and rabbits. 

Among the animals of the Nearctic Region that are found in cor- 
responding parts of Europe and Asia, in the Palearctic Region, are 
the formidable black bear, the reindeer, wolf, fox, beaver, squirrel. 

Among the more important of the fur-bearing animals are the 
lynx, the sea otter of the 
California coast, the er- 
mine, badger, silver fox, 
seal-mink, and beaver. 
The Hudson Bay Com- 
pany derives a consider- 
able income from traffic 
with the Indians in furs. 
Among the characteris- 
tic birds are the bald 
eagle, horned owl, wild 
turkey, grouse, and 
many species of ducks 
and geese. 

430. The Neotropic 
Region embraces a wide expanse ot forest, covering nearly half the 
region, a variety of open pasture lands or grassy plains, and the 




Fig. 138.— Eagle. 



300 



PHYSICAL OEOORAPHY. 



great mountain region of the Andes. In addition, it includes the 
tropical regions of the West Indies, Mexico, and Central America. 

Its fauna is characterized both by a great variety of types and 
a preponderance of peculiar types. So numerous are the forms of 
vertebrate life that, according to Wallace, at least one-half of all 
known fauna is represented. Among its characteristic animals are 
the flat-nosed South American monkeys, of species distinct from 
those of the Old World. These monkeys possess two additional 
molar teeth in each jaw and a well -developed prehensile tail. 
Among other animals are the blood-sucking bats or vampires, the 
chinchilla, inhabiting the Andean slopes, sloths, armadillos or mailed 
ant-eaters, the jaguar, ocelots, and other cats, cavies and agoutis, 
several varieties of deer, the peccary, and the tapir. The camel of 
the Eastern Continent is here represented by the llama, alpaca, and 
the vicuna. 

Birds are found in great variety and of peculiar species, such as 
humming-birds, trumpeters, macaws, toucans, currassows, beautifully 

variegated trogons, and 

-y ^ i^ the rhea, an approach 

to the ostrich. The 
condor is found in 
the higher mountain 
regions. 

Eeptiles are repre- 
sented by the giant, boa- 
constrictor, anaconda, 
coral snake, alligator, 
and a great variety 
of lizards. Insect life 
is exceedingly rich and 
varied. 

431. The Palearc- 
tic Region. — Though of enormous extent, reaching as it does from 
east to west, through nearly one-half of the entire circumference of 
the earth, yet the absence of north and south barriers permits so 




Fig. 139.— Alligator. 



ZOOLOGICAL QEOORAPHY. 



301 



%i-^ 




Fig. 140.— Camel. 



wide a range of its fauna that, according to Wallace, the majority of 
genera in countries so far sep- 
arated as Great Britain and 
Northern Japan are identical. 
The vast elevated semi-desert 
regions of Central Asia, how- 
ever, possess a few character- 
istic animals, among which the 
yak is the most important. 

Among quadrupeds, sheep 
and goats form a distinctive 
group. Here we find the ibex, 
moufflon, and chamois. The 
two-humped camel is peculiar 
to this region. Deer are rep- 
resented by the red deer, the 
musk deer, the reindeer, and elk. The European bear, polar bear, 
and beaver are also found. Among other distinctive mammals are 
the mole, badger, antelope, dormouse, and hare. Many of the fur- 
bearing animals common to the Nearctic Region are also found here. 

432. The Ethiopian Region embraces in its physical peculiari- 
ties a vast desert tract in the north, and a region of great equatorial 
forests, together with belts of open prairie land. This region comes 
next to the Neotropical in the number and variety of its animals. 
According to Heilprin,the 
African fauna is charac- 
terized by the remarkable 
development both of its 
carnivorous and its hoofed 
animals, and by the pecu- 
liarities presented by its 
quadrumana. 

The carnivora of the 
Ethiopian region are repre- ^^^- 141-— Lion, 

sented by the African lion, leopard, panther, hyena, jackal, and wolf 




302 



PHYSICAL GEOGRAPHY. 



>i^d^^' 




Among its hoofed animals the giraffe is peculiar to the region. 
The buffalo ranges over a wide extent of territory. Antelopes show 

an extraordinary devel- 
opment with very nu- 
merous species, repre- 
sented by animals vary- 
ing in size from the eland, 
whose dimensions ap- 
proach those of an ox, 
to the guevi, of the size 
of a rabbit. Other an- 
telopes are the gazelle, 
the water-buck, koodoo, 
bush-bok, blauwbok, 
gemsbok, blessbok, 
hartebeest, gnu, and 
springbok. 

Of horse-like animals 
are found the zebra, 
The quadrumana are represented by man-like 
apes, gorillas, chimpan- 
zees, and a great variety 
of monkeys. In Mada- 
gascar, which possesses a 
peculiar fauna, we find a 
development of the lem- 
urs, curious, monkey-like 
nocturnal animals, as well 
as true monkeys. 

The African elephant, 
a peculiar five-toed ani- 
mal, is also found in 
this region. The hip- 
popotamus is found in nearly ail the great rivers ; and several species 
of rhinoceros occur. 



Fig. 142.— Gazelle, 
quagga, and wild ass. 




Fig. 143.— Elephant. 



ZOOLOGICAL OEOGRAPHY. 303 

Birds. — Among some of the characteristic types are the bee-eaters, 
turacos, plantain-eaters, horn-bills, warbling finches, the ostrich, the 
secretary bird, a great variety of parrots, and many grouse. 

Reptiles include the deadly poisonous puff-adder, the rock boa, 
and the python ; among lizards, the crocodile and the chameleon. 

433. Oriental Region. — Here an exceedingly luxuriant tropical 
forest covers much of the country, while open pasture lands are 
found in some of the larger river valleys. 

The fauna presents some resemblances to African types, but the 
antelopes are replaced by the solid-horned ruminants, such as the 
deer, of which several varieties exist. 

The Oriental region was the original home of most of our com- 
mon domestic animals. Here occur the zebu, known generally as 
the sacred cow, or Brahmin bull, and several species of swine. 
Among carnivora we find the lion, tiger, leopard, panther, ounce, 
and fox. Here, also, is the home of the Indian or three-toed 
elephant. Quadrumana are represented by anthropoid apes, such as 
the orang-outangs and long-armed gibbon. 

Bird life is exceedingly rich in this region. Characteristic exam- 
ples are the bulbul, tailor bird, bee-eater, sun birds, birds of paradise, 
parrots, and many species of pheasants. The chicken is a native of 
this region. 

Among reptiles occur the giant python, cobra, vipers, lizards, and 
crocodiles. 

434. Australian Region. — This island continent is a moderately 
elevated plateau, so poorly watered that much of the west and cen- 
tre is practically a desert. On the east and south-east the land is 
well watered and is covered with rich forests. Both Papua and 
New Zealand are also well-watered mountainous districts. A narrow 
but deep strait, separating the islands of Bali and Lombok, forms 
part of a sharply marked boundary between the Australian and the 
Oriental region. Although but fifteen miles wide, it acts as an 
effectual barrier to the dispersal of the adjacent fauna. 

The Australian region possesses a very remarkable fauna. Its 
marsupials, the kangaroos and their allies, are wonderfully devel- 



304 



PHYSICAL QEOQRAPHY. 




oped. The kangaroo is represented by a great variety of forms: 
carnivorous, insectivorous, and herbivorous, varying in size from the 
great kangaroo to the diminutive kangaroo rats. The female kan- 
garoo, like other marsupials, is provided with a sack or 
pocket for carrying its immature young. 
The ornithorhyncus, or duck-bill, and the native hedge- 
hog are remarkable Australian types. 

Birds present many peculiarities. Among them are 

the parrots, cockatoos, birds of paradise, lyre-birds, 

mound-builders, cassowaries, ground-pigeons, 

and the great kingfisher. 

On the whole, the Australian species appear 

to present striking similarities to those of 

a prior geological age. 

435. Marine Fauna. — The ocean con- 
tains a marvellous va- 
riety of life, found mainly 
at or near the surface, 
or on or near the bot- 
tom. Marine fauna may, 
therefore, be arranged under three classes : 

(1) Littoral Fauna, or that of the shallow waters near the coasts. 

(2) Pelagic Fauna, or that of the surface waters. 

(3) Abyssal Fauna, or that of the ocean bottom at all depths. 

A careful study by Wyville Thomson of the collection made during the cruise 
of the " Challenger" has led him to the following conclusions concerning marine 
fauna : 

That at no part is the ocean devoid of life, either at or near the surface, nor 
on or near the bottom. An intermediate zone exists between the surface and 
the bottom, in which the larger forms of life are either nearly or entirely absent. 

That below the depth of 500 fathoms (3000 feet) marine fauna present the 
same features throughout all latitudes. 

That marine life is more abundant at moderate than at great depths. 

That the abyssal fauna is more nearly related to the fauna of the tertiary and 
secondary periods than is the pelagic fauna. 

That the characteristic abyssal fauna is most nearly related to extinct forms, 
and seems to occur in greatest abundance and of largest size in the Southern 



Fig. 144.— Kangaroo. 



ZOOLOGICAL GEOGEAPMY. 



305 



Ocean ; and that the general character of the fauna of the Atlantic and Pacific 
seem to indicate that the migration had taken place in a northerly direction. 

436. Littoral Fauna. — This embraces those creatures that live 
near the coasts in water of moderate depth. Most of these species 
have an exceedingly limited distribution, being confined to tidal 
pools or coral reefs, though some are found far from the shore, and 
may be almost regarded as pelagic. Some fishes, such as the salmon, 
shad, and striped bass, ascend rivers during the spawning season, 
and are called anadromous fishes. Some species are peculiarly 
adapted for life in the quiet waters of sheltered lagoons, and 
some for the tuibulent waters of the surf. 

437. Pelagic Fauna. — Creatures belonging to the pelagic fauna 
are found most frequently in great swarms or schools. Such ani- 
mals have developed great 
power for swimming, being 
able to traverse great dis- 
tances. They are compara- 
tively inconspicuous, their 
color differing but little 
from that of the water in 
which they live. Some are 
found at times in limited 
districts which they visit 
either while spawning or 
for food. Some important 
pelagic fishes are the mackerel, herring, tunny, dolphin, flying-fish, 
and some species of sharks. 

438. Abyssal Fauna. — These low forms of life are found in or 
near the bottom at all depths. Owing to the uniformity in tem- 
perature of the ocean water at moderate distances below the surface, 
abyssal species are practically the same in all latitudes. The ani- 
mals are of uniform dark color, with soft bodies. The eyes are 
either exceedingly large or are practically absent, the animal then 
having a highly developed sense of touch. In some cases the animals 

light the surrounding waters by means of a phosphorescent glow. 
20 




Fig. 145.— Seal. 



306 PHYSICAL GEOGRAPHY, 

CHAPTER II. 
The Distribution of the Human Race, 

439. Ethnography is that branch of physical geography which 
treats of the various races of men and their geographic distribution. 

Man has a much wider range than that of any of the lower ani- 
mals. He can adapt himself to all climates from the equatorial 
to the polar regions. This arises mainly from his superior intelli- 
gence, which enables him to procure clothing and shelter to suit bis 
varied environment. 

440. Unity of the Human Race. — Although the different races 
of men vary greatly in color, countenance, stature, and intelligence, 
yet it is now generally believed, by those who have carefully studied 
the subject, that they were all derived from a single species ; i. e., 
they are all brethren of a single family that very many generations 
ago lived together in a limited portion of the globe. Just where 
this cradle of the race was situated is uncertain ; but as the descen- 
dants of the first pair became too numerous for comfortable exist- 
ence within their narrow limits, there began a dispersal, or migra- 
tion, that has continued until practically all parts of the world have 
been occupied. 

At different times during this dispersal various groups of the 
wanderers became more or less isolated from each other. When 
this isolation was sufficiently prolonged, the changed conditions 
of food and climate resulted, during long periods of time, in 
such marked variations from the original type that there were 
finally produced the different races of men now found in widely 
separated parts of the world. 

441. Proofs of the Unity of the Human Race.— Among the 
circumstances that point to the descent of the human race from a 
single ancestry are: 

(1) The anatomical structure is invariably the same in all races. 

Kollmann, writing in 1883 concerning the anatomical test of unity, and refer- 
ring to Cuvier's statement, that it is possible to determine, from the examination 



THE DISTBIBUTION OF THE HUMAN RACE. 307 

of a single bone, the species to which any animal belongs, says : " Precisely on 
this ground I have mainly concluded that the existence of several human species 
cannot be recognized ; for we are unacquainted with a single tribe from a single 
bone of which we might with certainty determine to what species it belonged." 

(2) Gradual modification of types presented by the different races. 
The more marked outward peculiarities, which serve as a basis for 
classification, pass into each other by almost insensible gradations 
from the highest race to the lowest. This points to a gradual modi- 
fication of a single original race, through isolation under changed 
geographical conditions, that resulted in the present racial types. 

Concerning this point Blumenbach writes as follows: "Although between 
distant peoples the difference may seem so great that one may easily take the 
inhabitants of the Cape of Good Hope, the Greenlanders, and Circassians for 
peoples of so many distinct species, nevertheless we shall find, on due reflection, 
that all, as it were, so merge one in the other, the human varieties passing grad- 
ually from one to another, that we shall scarcely, if at all, be able to determine 
any limits between them." 

(3) Folk-lore. — The similarity of the earlier myths, legends, 
customs, proverbs, superstitions, games, etc., shown by the modern 
science of folk-lore to exist among tribes separated by thousands 
of miles, renders it highly probable that the early ancestors of 
these races once lived together, since it is extremely unlikely that 
tribes that had never been in contact, could have independently 
evolved and handed down to their descendants similar legends, 
myths, etc. 

(4) Close Resemblance of Language of Widely Separated Races. — 
If we examine the words used in different nations to express the 
most common ideas, we will find a remarkable similarity between 
many of them. For example, the words for father, mother, sister, 
brother, and God show a remarkable general similarity. An ex- 
tended comparison made in this way between different languages 
has shown a common origin of the languages of Europe and of a 
large part of Asia. It has been shown that these tongues appa- 
rently owe their origin to a single parent nation which dwelt during 
prehisioric time somewhere in South-western Asia. 

^ But other families of language, such as the Chinese, Semitic, African, Amer- 



308 PHYSICAL GEOGBAFHr. 

ican Indian, and others, covering a vast multitude of peoples inhabiting large 
areas of the earth, show no resemblance or similarities, but constitute distinct 
or so-called stock latiguages. Keane, speaking of this fact, says: "Thus the 
existence of the present stock languages is no argument at all for the disparity 
of the human family ; while, on the other hand, the fact that every single mem- 
ber of that family is a speaking animal, supplies, perhaps, the very strongest 
argument for the specific unity of all its branches." Waitz aptly remarks that 
inasmuch as the possession of a language of regular grammatical structure forms 
a fixed barrier between man and the brute, it establishes at the same time a 
near relationship between all peoples in psychical respects. . . . "In the pres- 
ence of this common feature of the human mind, all other differences lose their 
importance." 

The argument for the unity of the human race is thus briefly 
summed up by Dr. E. B. Tyler: 

" (1) That all tribes of men, from the blackest to the whitest, the 
most savage to the most cultured, have such general likeness in the 
structure of their bodies and the working of their minds as is easiest 
and best accounted for by their being descended from a common 
ancestry, however distant. 

" (2) That all the human races, notwithstanding their form and 
color, appear capable of freely intermarrying and forming crossed 
races of every combination." 

4A2. Degree of Civilization. — Among different races of men 
profound differences exist in the degree of their civilization ; i. e., 
they are savages, barbarians, semi-civilized, or civilized. The causes 
for these differences may, to a great extent, be traced to varying 
geographic conditions ; i. e., to the effect that the character of a 
country has on the life of its iuhabitants. In his early life man, 
probably, existed as a hunter and fisher. When a rich soil and . 
favorable conditions existed, he was apt to become a tiller of Jthe 
ground, and was necessarily restricted to a limited area. Even in .his 
earliest existence a necessity for some sort of shelter or home led 
to rude architectural efforts. When a tribe became agriculturists, 
their houses were improved, because they then became fixed hornes. 
With this came the domestication of animals, such as the dog, horse,' 
cow, etc. Then came the association of people in towns or cities, - 
the location of which depended on geographical conditiotis. cThe 



J 



100 180 



140 120 




Longitude 140 East from ICO Greenwich 180 




LiiDgitude 20 Etxst from 40 Greenwich CO 



100 120 



THE DISTRIBUTION OF THE HUMAN RACE. 309 

wants of such commuuities led to improvements in the arts, and 
in this way man eventually became highly civilized. 

Where, however, as in comparatively early times, the conditions 
were unfavorable to the settled life of the tiller of the ground, but 
rather favored the keeping of flocks and herds, there was necessi- 
tated a wandering life, which prevented an advance in civilization 
beyond that of the barbarian. 

443. The Races of Men. — Various classifications have been 
proposed for the division of the human species into races. We 
will follow, generally, that adopted by Brinton, Meade, and others, 
based on the color of the skin and peculiarities of the hair and 
nose, which divides man into the following races : The Caucasian 
or White Race ; the Mongolian or Yellow Race ; and the African or 
Black Race 

444. Characteristic Physical Traits. — Caucasia^i Race. — 
White skin, varying from darker to lighter tints, as seen in bru- 
nette and blonde types ; wavy hair ; narrow nose. 

Mongolian Race. — Yellow or brownish-yellow skin ; straight hair; 
medium nose; i. e., neither narrow nor flat. 

African Race. — Black skin ; hair woolly or crinkled ; nose flat. 
: The Caucasian, Mongolian, and African races are sometimes 
called the primary races. 

The Australian race and tlie Malay or brown race are believed 
by some to be modifications of the African or black race. The 
Malays by others are believed to be modifications of the Mongolian 
race. The American or red race is believed to be a modification 
of the Mongolian race. 

The Australians, the Malays, and the American Indians are some- 
times called the secondary races. 

The highest civilization is found in the Caucasian race ; the lowest, 
probably, in the African race. 

445. The Caucasian or "White Race. — This race name was 
applied to the white race when the original home or cradle of the 
race was believed to be somewhere in the neighborhood of the 
Caucasus Mountains. Later studies have led some to trace the 



310 



PHYSICAL GEOGRAPHY. 



original home of this race to somewhere in Southern Europe, 
or in Northern Africa, and to find the purest type of the white 
race, not in the Caucasian, but in the Berber peoples, inhabiting 
some of the valleys of the Atlas Mountains. 
These call the white race the Euafrican, but 
as this conclusion is not generally adopted, 
we retain the name Caucasian. 

The Caucasian or White Race includes 

the inhabitants of Northern Africa, 

South-western Asia, all of Persia and 

Arabia, part of Hindostan, and nearly 

all of Europe. The descendants of the 

race now people large parts of both 

North and South 

America, Australia, 

and Southern Africa. 

The Caucasian race 
may be conveniently 
divided into the South 
Mediterranean branch, 
including the Hamitic 
and Semitic branches, 
and the North Medi- 
terranean branch, in- 
cluding the Aryan or 
Indo-European branch. 
Nearly all the most 
highly civilized peoples 
of the world have de- 
scended from the Aryan 
race. 
446. South Mediterranean Branch of the White Race. 
The Hamitic Stock of this branch of the Caucasian race occupies 
all the northern and north-eastern parts of Africa, including the 
Barbary States, the Sahara, and a considerable area south of the 




Primary 
Races. 



Fig. 146 



Euro- 



I 



THE DISTRIBUTION OF THE HUMAN RACE. 



311 




Fig. 147.— Caucasian — Arab. 



desert, together with parts of Abyssinia. Some of the ancient 
peoples of this branch included the Numidians, Libyans, Etrus- 
cans, Amorites, and the Assyrians. Some of the modern peoples 
are the Berbers, Zouaves, Kabyles, 
Tibbus, Copts, Fellaheen, Gallas, and 
Somalis. 

The Semitic Stock occupies Arabia, 
part of Abyssinia, and Syria. Some 
of the ancient peoples of this branch 
were the Israelites and the Chaldeans, 
Abyssinians, Arabs, and Bedouins. 
Some of the modern peoples are 
the modern Arabs, Bedouins, Gheez, 
Ethiopians, the modern Israelites, and 
Samaritans. 

447. North Mediterranean 
Branch of the "White Race in- 
habits all the remainder of the re- 
gion. The early progenitor of this branch of the race, traced by 
some to Japhetic origin, is not certainly known. The most im- 
portant stock of this branch of the Caucasian race was the Aryans, 
who during early times occupied Southern and Central Europe and 
parts of Asia. It was branches of this people who, in the valleys 
of the Indus and the Ganges, laid the foundation of the ancient 
civilization of India. Other branches of the race further to the 
west laid successively the foundation of the highest civilizations of 
antiquity, those of Greece and of Rome. 

The principal groups of the Aryan stock are the — 

Celtic Group, including the Irish, Welsh, and Scotch, and the 
Bretons of France. The ancient Gauls were of this group. 

Italic Group, including the Italians, Spaniards, Portuguese, French, 
Roumanians, Wallachians. The ancient Latins and Sabines be- 
longed to this group. 

Ulyric Group, including the modern Albanians and the ancient 
Illyrians and Thracians. 



312 



PHYSICAL GEOGRAPHY. 



Hellenic Group, including the ancient and mod^Ti Greeks. 
Teutonic Group, including among modern peoples the Scandiua 
vians, Germans, Danes, Dutch, English, Anglo-Americans, and 
among ancient peoples the Goths, Vandals, Franks, Angles, and 
Saxons. 

Slavonic Group, including among others the Russians, Poles, 
Czechs, Servians, Croatians, Bulgarians, and the Montenegrins. 

Indo-Iranic Group, including among others the Armenians, Per- 
sians, Hindoos, Kafirs, Beluchis, and Gypsies. 

The Caucasic Stock includes the many small tribes inhabiting the 
defiles and fastnesses of the Caucasus Mountains. Here a surpris- 
ing diversity exists in racial types 
and languages. The Circassians, the 
Georgians, and the Mingrelians are 
among the more important. 

In addition to the above there is 
the Uskaric stock, including the 
Basques, who live in the valleys of 
the Pyrenees, both in France and 
Spain. Their language is interesting 
as belonging to the primitive forms of 
speech such as are found among the 
Negroes of Central Africa or the sav- 
age tribes of Siberia. 

448. Geographic Influences. — Abundant evidence of the influ- 
ence of geographic conditions on the civilization of man is found in 
the different peoples of Caucasian stock. For example, the isola- 
tion afforded Hindostan by the Himalayas undoubtedly aided the 
development of Indian civilization. Similarly, the Alps and the 
Apennines isolated the early civilization of Rome. England, favored 
with uninterrupted water communication with practically all parts of 
the world, has developed its commerce to a remarkable extent. 

449. The Mongolian or Tello-w Race inhabits practically all 
the Continent of Asia not occupied by the Caucasians. There are 
two branches of the Mongolian race : the Sinitic and the Sihiric, 




Fig. 148. — Caucasian — Hindoo. 



THE DISTRIBUTION OF THE HUMAN RACE. 313 






_^L 



_ rm .^ 



450. The Sinitic Branch, or, as the word means, the Chinese 
branch, includes, besides the Chinese, its typical members, the Thi- 
betans and the inhabitants of Bur- 
mah, Siam, Annam, Cambodia, Co- 
chin China, and Tonquin. 

4-51. The Sibiric Branch ; i. e., 
the Siberian branch, occupies the 
continent north of the Mongolian 
plateau from the Baltic and Black 
Sea to the Pacific and its neigh- 
boring island chains. It in- 
cludes the Tungus and the 
Manchus. The latter 
people conquered China 
in the seventeenth cen- 
tury, and have held it 
since that time. The 
Sibiric branch also in- 
cludes among others the 
Mongols, who inhabit the 
semi-deserts of the Mon- 
golian plateau, the Kal- 
mucks, the Turcomans, 
Yakouts, Turks, a Mo- 
hammedan tribe now oc- 
cupying European and 
Asiatic Turkey, Cossacks, 
and Huns. Other groups 
include the Finns, Lapps, 
and Magyars, the Samo- 
yeds, Yakouts of Northern 
Siberia, the Koraks, Kamt- 
chatkans, and the Japanese 
and Koreans. The Japanese are the most highly civilized people 
of the yellow race, having, by deliberate adoption, added to their 




Fig. 149.— Mongolian- 
Chinese. 



314 



PHYSICAL GEOGRAPHY. 



native civilization, itself of no mean order, the most advanced Cau- 
casian civilization. 

463. The Geographic Influences on the yellow race, on the 
whole, have tended to retard or arrest its highest development. 

The vast extent of 
elevated plateaus 
bordered by high 
mountain walls, sup- 
plied with a rainfall 
so scanty as to render 
the district a semi- 
desert ; its vast ex- 
tent of inhospitable 
tundras on the north 
and other poorly 
drained plains, to- 
gether with the com- 
paratively few fertile 
river valleys, have 
not favored the de- 
velopment of a very 
high civilization over 
most of the region. 
453. The African or Black 
Race occupies all the con- 
tinent of Africa and Austra- 
lia not inhabited by the Cau- 
casians, most of the islands of 
the Malay Archipelago, and 
the Polynesian island chains. 
That part of the race inhabit- 




Fig. 150. — Mongolian — Japanese. 



ing the Continent of Africa is 
divided into three branches: the Negrillo, the Negro, and the 
Negroid. 

454. The Negrillo or Little Neg-ro Branch comprises an 



THE DISTRIBUTION OF THE HUMAN RAGE, 315 




unusual variety of small men, generally known as the Pygmies, 
inhabiting the forests north of the Congo. The Pygmies include 
the Akkos, Tikki-tikkis, and others. They live by hunting and 
fishing, having no settled homes. Other peoples of the JSTegrillo 
branch, the Bushmen and Hottentots, are found in the southern 
part of Africa, on the border of 
the Kalahari desert. They are of 
larger stature than the pygmies. 

455. The Negro Branch of the 
race includes the true Negroes 
who live in the Soudan and its 
adjoining country. The principal 
groups of this branch are the Ni- 
lotic Group, including the inhabi- 
tants of the Egyptian Soudan and 
the White Nile, the Soudanese 
Group, including the inhabitants 
of the Central Soudan, and the 
peoples living around Lake Tchad,- 
or on the banks of the Niger River, 
on which populous cities, such as Sousandig and Timbuctoo, have 
been built. The Senegambian Group includes the inhabitants of 
the Senegal River in Senegambia in the Western Soudan. Thi 
Mandingoes occupy an extensive region lying between Western 
Guinea and the country near Timbuctoo. The Guinean Group 
includes the inhabitants of the coast of Guinea. The names of 
these tribes are unfortunately known to us chiefly because of 
their situation in the centre of the slave-trade region. 

456. The Negroid Branch lacks some of the characteristic traits 
of the race, and, probably, consists of peoples resulting from the 
intermarriage of true negroes with Haraitic or Semitic types. They 
include the Nubian Group, whose people are for the greater part 
pastoral tribes, found along with the white race on both sides of 
the Nile between the first and second cataracts ; the Bantu Group, 
whose people occupy nearly all of Africa south of the equator, except 



Fig. 151. —African— 2ulu. 



316 



PHYSICAL GEOGRAPHY. 




that i^art occupied by the Bushmen and 
the Hottentots. This group includes the 
Caffirs, on the eastern coast, the Bechuanas 
west of the Caffirs, the Zulus, and the 
tribes of the Congo basin 
and the Zambesi. The 
Caffirs have large herds 
of cattle, and practise 
agriculture to a limited 
extent. The Congo 
Free State includes the 
inhabitants of the basin 
of the Congo River, a 
region over ten million 
square miles in area- 
It comprises a number 
of independent native 
tribes. 

457. Geographic In- 
fluences. — The influence of 
geographic conditions in Africa, 
on the development of the black 
race, has been that of the tropics 
generally. The lavish profusion 
with which nature supplies food, 
with little or no effort on the part 
of man, has materially retarded the 
progress of the race. 

As regards geographic conditions 
on the remaining branches of the 
African race, we find, in the 
diversity of type and languages pre- 
sented, the natural result of the isola- 
tion to which insular peoples have to a 
greate*- ->r less degree been subjected. 



THE DISTRIBUTION OF THE HUMAN RAGE. 



317 



m^^^mME 



'osa^o,&^a59Sog5; ^n>a^'cQ^waiSfe-^^^o0jV. 



Fig. 153.— Malays— Filipinos. 






458. Secondary Races.— The Australian Race, a modifica- 
tion of the African race, includes the natives of Australia. The 
Dravidians, or primitive inhabitants of South-eastern Hindostan, 
are also allied to this race. The Dravidians vary from black to 
brown-black in color, have large, flat noses, bushy, wavy black 
hair, and full beards. They are 
probably the lowest in civilization 
of the race. 

459. The Malay or Brown 
Race includes peoples possessing 
marked contrasts. For conveni- 
ence they may be divided into the 1 1 
Malayic and the JSTegritic branches 

The Malayic Branch consists 
of two groups : the Malayan or 
Western peoples and the Poly 
nesian or Eastern peoples. 
The Malayan Group in- 
cludes the Malays of 
Malacca and Sumatra, 
the Javanese, the Bat- 
tacks of Sumatra, the 
Dyaks of Borneo, and 
the Hovas of Mada- 
gascar. The Polynesian 
Gro up includes the 
Maoris of New Zealand, 
the inhabitants of the 
Tongan Islands, and the 




inhabitants of Polynesia 
generally. 

460. The Negritic Branch includes the Negrito Group, the 
Papuan Group, and the Melanesian Group. The Negrito Groups 
includes the inhabitants of the Andaman and Nicobar Islands and 
of the Philippine Islands generally. The Papuan Group inclijdeS 



318 



PHYSICAL GEOGRAPHY, 



the inhabitants of Papua or New Guinea. They are very low in 
civilization. The Melanesian Group includes the natives of the Fiji 
Islands, New Caledonia, Loyalty Islands, and the New Hebrides. 

461. The American or Red Race includes all the inhabitants 
of North and South America not embraced in the Caucasian or 

Ethiopian races. This 
race includes a number 
of groups. 

The Arctic Group 
includes the Eskimos 
inhabiting the Alaskan 
and the Aleutian 
Islands. 

The North Atlantic 
Group includes the 
Indians of North 
America south of the 
Arctic Group from the 
Atlantic to the Rocky 
Mountains. These peo- 
ples are gradually dis- 
appearing before the 
whites. 

The North Pacific 
Group includes the va- 
rious tribes, west of the 
Rocky Mountains, from 
Mt. St. Eli as to Lower 
California and Mexico. 
It includes the Pueblo 
Indians and the cliff 
dwellers of South-west- 
ern United States. These tribes have attained a fairly highly devel- 
oped state, but, like the peoples of the preceding group, have mainly 
disappeared. 




Fig. 154. — American— Indians. 



MINERALS. 319 

The Mexican Group. — The leading peoples of this group, the 
Aztecs and the Central American Groups, including the inhabitants 
of Tehuantepec and Panama, reached a high degree of civilization, 
as is shown by the ruins of their wonderful architectural achieve- 
ments. 

The South Atlantic Group includes the former peoples of the "West 
Indies, the Orinoco, the Amazon, and the La Plata. This group 
includes the Caribs of the Antilles, the Arawaks, of what now con- 
stitutes Guiana, and the Tapuyas of Brazil. Numerous tribes peo- 
pled the plains of the Pampas, while on the extreme south are the 
Patagonians and the Fuegians, very low in civilization. 

The South Pacific Group includes the ancient peoples of the Andes. 
They had reached a high civilization when conquered by the 
Spaniards. 

SECTION III. 
MINERALS. 



-oj^^c 



CHAPTER I. 

Minerals. 

462. Distribution of Minerals. — Although some mineral sub- 
stances, such as coal, are limited to the rocks of certain geological 
formations, yet the majority occur in the rocks of all formations, 
as mineral veins, lodes, or local ore deposits. 

A vein is a general name applied to the gradual filling with min- 
eral matters of fissures, or more or less open spaces in the rocks. 
When the fissure is immediately filled by an injection of molten 
rock, it is called a dylce. 

Vein matter is usually crystalline. The most common vein material 
is quartz. Feldspar, granite, and calcite are also common vein mat- 



320 PHYSICAL GEOGRAPHY. 

ters. A vein containing metallic ores is called a lode. The earthy 
minerals associated with the ore are called the gangue. 

The most common metallic ore in veins is pyrites or iron sulphides. 
Some metallic substances, such as gold, silver, copper, platinum, and 
bismuth, occur in the pure or native state. 

4:63. Varieties of Veins. — Veins are either — 

(1) Veins of Segregation, or veins in which no sharp lines of sepa- 
ration appear between the vein matter and the rock which the vein 
encloses. These veins have no distinct boundaries or walls. 

(2) Veins of Infiltration, or small fissures or lines of fracture, filled 
usually with deposits of mineral substances from slowly percolating 
waters. These veins have distinct walls, since they result from the 
gradual filling of distinct fissures. 

(3) Fissure Vems, or fissures extending to great depths that have 
been gradually filled in various ways by mineral deposits. These 
have distinct walls and usually occur in parallel systems, and 
outcrop or extend over the surface for many miles ; their depth is, 
probably, profound. 

464. Some Peculiarities of Fissure Veins. — One of the ways 
in which fissure veins were filled with metallic substances was by 
means of vapors or hot solutions coming up from below. In this 
way were formed the rich copper deposits of the Lake Superior 
region, and, perhaps, the richest part of the silver, copper, and lead 
veins of the western part of the United States. These vapors or 
hot alkaline solutions came up through the fissures and were deposited 
either in the fissures or in cavities in neighboring rocks. Limestone, 
which is easily corroded, frequently bears rich mineral deposits near 
its junction with mineral veins. 

By far the greater part of the metallic deposits or ores that are 
extensively mined occur in great fissure veins. Some, such as iron 
ores, occur in extended deposits which originally collected in the 
bottoms of marshes or bogs. Others, such as lead, accumulate in 
flat cavities, between parallel strata, especially in limestone districts. 
All veins may contain metallic, ores, but it is only the deposits of 
great fissure veins that are extensively mined, since those which 



MINERALS. 321 

occur in veins of segregation are, as a rule, too irregular, and those 
in veins of infiltration too small, to be profitable. 

Usually only a small part of a vein contains metallic ores, the 
greater part being filled with various vein stufis or gangues. The 
metallic ores occur in various parts of the vein, either in ribs or 
sheets, in bunches or pockets, or in small stringers or veins. 

Fissure veins do not maintain the same width throughout all parts 
of their length, but widen in some places and narrow or pinch in 
others. Sometimes the vein will enclose a part of the rock of which 
the wall of the vein is formed. This mass, so isolated, is called a horse. 

465. Value of Mineral Products. — The civilization of man is 
largely dependent on the extent and character of the earth's mineral 
deposits. Man's progress would have been seriously retarded had 
there been no metals from which he could fashion tools, build ma- 
chines, form the rails for steam and electric railroads, draw wires for 
the electric conductors for telegraph, telephone, electric light, or 
power lines, or none suitable for coinage and ornamentation. Espe- 
cially would he have been severely handicapped had there been no 
stores of energy placed in the earth in the shape of beds of coal, 
peat bogs, or recesses filled with petroleum or natural gas ; or had he 
failed to find, in the earth, beds of granite, marble, sandstone, and 
other similar materials, with which to build his houses ; and if 
the mineral products now employed for their curative properties 
were denied to him, life and health would have been seriously 
decreased. 

466. Varieties of Mineral Substances. — Mineral substances 
occur generally as solids, either in the pure or native state ; or as 
ores ; i. e., associated or combined with other substances, as sulphides, 
oxides, carbonates ; or as various building stones, coal, rock-salt, 
metals, etc. They occur also as liquids, such as petroleum or coal- 
oil ; or as various mineral waters ; or as gases, as in the case of 
natural gas. 

Metallic ores occur usually in veins or in local ore deposits at 
various depths ; the latter are sometimes found at the surface, and 
are then obtained by simple quarrying ; more frequently, however, 
21 



322 PHYSICAL QEOGBAPHY. 

they occur in veins at considerable depths below the surface, in which 
case shafts are sunk in the vein, and at certain depths are cross-cut 
to the walls of the vein, and then cuttings or galleries are made 
along the vein in what are called drifts or levels, the levels being 
numbered from the surface, as the 1st, 2d, 3d, etc. 

In the case of gold mining, if the ore is free-milling ; i. e., consists 
of metallic gold distributed in fine particles through quartz or other 
gangue — it is reduced to a powder by stamp mills or other means, 
and extracted by agitation in water, aided by amalgamation with 
mercury. With some ores a cyaniding process is used. This process 
is based on the affinity for gold possessed by very dilute, aqueous 
solutions of cyanide of potash in the presence of air. In other cases 
the gold is extracted by smelting ; i. e., mixed with fluxes and carbon 
and subjected to great heat. In placer deposits — where small par- 
ticles of gold are distributed through large beds of decomposed 
rock — hydraulic mining is employed, powerful streams of water 
being used to wash down the decomposed rock. 

467. Classification of Mineral Products. — For convenience of 
study, mineral products may be divided into the following classes: 

(1) The metals and their ores. 

(2) Non-metallic substances, which may be conveniently sub- 
divided as follows : 

(a) Coal, peat, petroleum, natural gas, and asphalt. 
(h) Clay, kaolin, marl, salt, cements, phosphate rocks, borax, 
Bulphur, etc. 

(c) Building stones, etc. 

(d) Precious stones or gems. 

468. The Metals and their Ores. — The most important metals 
are iron, copper, gold, silver, lead, zinc, aluminium, mercury, anti- 
mony, nickel, platinum, tin, etc. 

Iron, the most useful and indispensable of all the metals, is, 
perhaps, the most widely distributed. Its principal ores are various 
oxides and carbonates. The ore is reduced to the metallic state 
by heating in blast furnaces while mixed with coal and limestone. 
Pig iron, the name given to the product obtained from the blast 



MINERALS. 323 

furnace, is refined either by remelting, thus producing cast iron; or 
by reheating the pig iron and forging and rolling it, thus changing 
it to wrought iron; or, as by the Bessemer process, by removing all 
the carbon from the cast iron, and then adding the amount of 
carbon required to produce steel. 

Extensive deposits of iron ore occur in the United States, which 
leads the world in the production of pig iron. Great Britain comes 
next in this regard ; then Germany, France, Belgium, other parts 
of Europe, and other parts of the world. 

Copper, probably, comes next to iron in its economic value. 
It occurs both pure or native, and in various ores, mainly sulphides, 
oxides, and carbonates. Copper is employed as wires for various 
electric conductors, or as plate copper for sheathing ships and 
buildings ; or, it may be alloyed with various metals, such as brass, 
bronze, gun metal, bell metal, etc. 

Probably the most valuable deposits of copper occur in the United 
States. Europe, especially Spain and Germany, South America, 
Japan, and Australia are also large producers. 

Gold owes its high rank in money value among the metals to the 
fact that it does not readily rust or tarnish on exposure to the air, 
and to the ease with which it may be wrought. It is, therefore, 
extensively employed for coinage and jewelry. Gold occurs most 
extensively in the metallic state in minute scales, or in small gran- 
ules or irregular masses called nuggets, found either in quartz 
veins, in the sand or gravel of river beds, or in alluvial deposits 
called placers. 

Gold is found in all parts of the world. The United States is the 
principal producer. Australia, Southern Africa, Canada, and Russia 
are all large producers. 

469, Silver, Lead, and Zinc. — Silver, like gold, does not readily 
rust or oxidize, but readily blackens on exposure to air containing 
sulphur fumes. Silver is largely employed for coinage and jewelry. 
It occurs both native and as various ores usually associated with 
gold, lead, or other metals. It occurs in connection with the gold- 
fields already mentioned. 



324 PHYSICAL GEOGRAPHY. 

Lead and zinc are valuable metals. Lead is extensively used for 
water-piping, lining tanks, bullets, etc. It forms valuable alloys, 
and, in the form of white lead, is used in the manufacture of paints. 
Zinc is employed extensively in the form of sheets, into which it is 
readily rolled ; for galvanizing or coating iron in order to prevent 
rusting; and in voltaic batteries. Zinc forms valuable alloys. Brass 
consists of an alloy of zinc with copper. 

Zinc and lead are frequently found associated. Their principal 
ores are the sulphides, called respectively blende and galena. In 
the United States the galena usually overlies the blende. Galena 
is frequently associated with silver. Extremely rich and valuable 
deposits of both zinc and lead are found in the United States, in 
Missouri. Germany and Belgium also contain extensive deposits. 

Aluminiura or aluminum is a remarkably light metal found 
in cryolith and clay. 

Mercury or quicksilver differs from all other metals by being 
liquid at ordinary temperatures. It is extensively employed in 
thermometers and barometers. Its power of readily forming an 
alloy with gold is utilized in the amalgamation process for extract- 
ing gold. An amalgam of mercury with tin is employed for the 
backing of mirrors. The principal ore is the sulphide or cinnabar. 
Deposits occur in Spain and in various parts of the United States. 

Antimony is extensively employed in the arts alloyed with lead 
as type metal. This alloy is valuable from the property it pos- 
sesses of expanding on solidifying from a fused condition, thus 
permitting it to take sharp casts. Valuable deposits of antimony 
occur in the United States. 

Nickel is a metal which, from the fact of its not readily tar- 
nishing, is extensively employed for electroplating iron and other 
readily oxydizable metals. German silver is one of its valuable 
alloys. It is employed to some extent in coinage. 

Platinum, one of the heaviest of the metals, occurs both native 
and alloyed with other metals. It is extensively used in the 
leading-in wires of incandescent electric lamps. Its extremely high 
melting-point renders it especially fitted for use in the construction 



MINERALS. 325 

of small vessels, such as crucibles or retorts, employed under certain 
circumstances at high temperatures. The principal deposits are 
found in the Ural Mountains. 

Tin is a well-known metal largely employed for common house- 
hold uses. Tin plate consists of sheets of iron covered with a thin 
layer of tin. The principal ore of tin is the oxide. Tin forms 
valuable alloys with other metals, such as pewter, bronze, and 
Britannia metal. The ore deposits of Cornwall, England, of the 
Straits Settlements, and of Bolivia, form the principal sources of 
supply of tin. 

470. Non-metallic Substances. — The most important non- 
metallic substance is coal. Coal-beds occur in nearly all parts of 
the world, but the greatest production has been from the deposits in 
the United States. Great Britain, Belgium, and Germany are also 
large producers. Undeveloped coal-fields exist in China, Peru, 
Alaska, Japan, and Mexico. 

Coke, employed in smelting metals, is produced by heating bitu- 
minous coal in closed ovens, and thus driving off its volatile con- 
stituents. Illuminating gas is made by the destructive distillation 
of soft coal ; i. e., by heating soft coal in closed ovens while out of 
contact with air. 

Coal Oil and Natural Gas are produced by the decomposition 
of vegetable or animal matter 
when protected from the atmos- 
phere by burial in the earth, 
and are usually associated with 
each other. The oil collects 
like water in reservoirs in 
porous strata, and frequently 
issues like springs from hill- 
sides. It is obtained from the 
reservoirs by boring. The Fig. 155.— Gas and Oil Deposits, 

wells so formed are simi- 
lar to artesian wells, except that the oil is thrown out in powerful 
streams by the pressure of the gas. The crude oil is stored in huge 




326 PHYSICAL GEOGRAPHY. 

tanks, from which it is transferred to barrels or to iron tanks for 
transportation, or it is distributed to great distances through lines 
of pipes called pipe lines. For most commercial uses, the oil is puri- 
fied or refined. 

The reservoirs contain water, oil, and gas, collected according to 
their differences of density, with the gas above and the water below, 
as shown in Fig. 155. A well sunk at W, will discharge water, 
frequently containing common salt in solution. A well at 0, will 
discharge oil, and one at G, natural gas. Usually the water, gas, 
and oil collect, not in open reservoirs as shown in the figure, but 
in the spaces between the particles of layers of sand or other finely 
divided material. 

The richest oil fields in the world are those of the United States 
and Russia. 

During the distillation of petroleum there are obtained a variety 
of by-products, such as gaaoline, naphtha, benzine, kerosene, and 
paraffin oil. A solid substance called paraffine, possessing excel- 
Jent electric insulating powers, is obtained by distilling paraffin 
oil. 

Asphaltum, or Mineral Pitch, frequently associated with petro- 
leum, occurs in various parts of the world. The island of Trinidad, 
where a large lake of asphaltum exists, furnishes a large proportion 
of the material employed for paving sidewalks and streets. Exten- 
sive deposits also occur in various parts of the United States, in 
South America, and in connection with the vast oil-fields of the 
Russian Empire. 

Peat is an inferior form of fuel already referred to in connection 
with the formation of marshes in cold, moist climates. Extensive 
peat bogs exist in Ireland and in the United States. 

471. Clay, Kaolin, Marl, Salt, Sulphur, and Graphite. — 
Besides the mineral products already described, there is a great 
variety of others that are employed for various purposes in the arts. 
Some of the more important of these are clay, kaolin, marl, salt, 
sulphur, cements, phosphate rock, borax, and graphite. 

Clay and kaolin aie extensively employed in the manufacture of bricks, pot- 



MINERALS. 327 

tery, terra-cotta ware, stoneware, china, and porcelain. Marls are various mix- 
tures of clay and lime, and are employed for fertilizing land. Clay and marls 
are extensively found in all parts of the world. Common salt, or chloride of 
sodium, is one of the principal saline ingredients in ocean water and in the 
waters of inland seas or steppe lakes. It occurs also in vast deposits as rock-salt, 
where it has been derived from the gradual evaporation of saline waters. 

Sulphur exists in a native or pure state in volcanic districts, or is gener- 
ally distributed combined with various metallic substances as sulphides. It is 
extensively employed in the manufacture of sulphuric acid. 

Graphite is a form of carbon extensively employed in lead pencils, and is 
valuable as a lubricant. 

In addition to the above mineral products are beds of sand, suitable, when 
mixed with burnt lime, to form mortars and cements ; or to form glass, when 
fused with potash or other basic substances. Valuable deposits of phosphate 
rocks are employed in the manufacture of fertilizers. 

472. Building Stones are found in immense deposits near the 
surface in various parts of the world. A material to be suitable for 
building purposes must possess great strength and tenacity, and, 
be able to resist being crushed by the weight placed upon it. It 
must especially resist disintegration or breaking up under the action 
of the weather. 

The more important building stones are granite, gneiss, blue-stone, 
sandstone, magnesian limestone, marble, and slate. 

473. The Precious Stones or Gems. — Besides the mineral sub- 
stances already referred to, which with some few exceptions occur 
in extensive deposits in nearly all parts of the world, there are 
others which either occur rarely ; or, if common, are seldom found 
in fine specimens, free from flaws or other blemishes. These min- 
erals are called the precious stones or gems, and are highly prized 
as articles of jewelry. 

The principal precious stones, or gems, are the diamond, the 
sapphire, the ruby, the topaz, the emerald, the beryl, the opal, and 
the garnet. 

The diamond is a crystallized form of pure carbon. Its value depends on its 
lustre and color, on its freedom from flaws, and on its size, especially the latter. 
In the natural state the diamond is without lustre, and requires to be cut and 
polished in order to bring out its lustre or fire. Its value is rated by the carat 
(approximately 3 grains). The prinoipal diamond-fields of the world are in 
South Africa, New South Wales, the Ural Mountains, and Brazil. 



328 PHYSICAL GEOGRAPHY. 

The sapphire is a beautiful blue stone ; the best specimens are found in BraziL 
The ruby has a deep red color; perfect specimens of more than two carats in 
weight are more valuable than the diamond ; the best specimens are found in 
Siam. The topaz is a yellow stone of various kinds ; the best specimens are found 
on Topaz Island in the Eed Sea. The emerald is a gem of a beautiful green 
color; the finest specimens are found in New Granada. The beryl is a stone 
which occurs in the form of six-sided prisms, usually, either blue, green, or yel- 
low, but sometimes colorless. The opal, with its changing hues and blending 
colors, possesses a strange beauty which is highly prized. The garnet occurs in 
a variety of colors and is quite abundant, being found in all the continents. 

Other minerals used for ornamentation and jewelry, but less valuable than the 
above, are turquoise, lapis-lazuli, malachite, and quartz. 

Quartz is a crystal stone of some beauty; amethyst, cat's-eye, chalcedony, 
onyx, sardonyx, carnelian, jasper, agate, blood-stone, plasma, and chrysoprase 
are varieties of quartz of different colors and markings. 

Pearls are deposits of carbonate of lime and organic matter; they are found 
within the shells of the pearl oyster and other moUusks ; they occur especially 
on the tropical coasts of Asia and America ; the best specimens are found on the 
coasts of Ceylon. 

SYLLABUS. 

Zoological geography, or zoogeography, treats of the distribution of animal 
Ufe. 

The animals of any section of country are called its fauna. 

Animals derive most of their food either directly or indirectly from plants, 
hence the existence of the fauna of any region is dependent upon its flora. 

When the animals of any section of country multiply so rapidly that their 
food supply becomes insufficient, they must either seek a new home or perish. 
This dispersal is onposed by certain physiographical or physiological barriers. 

The principal physiographical barriers are: (1) Large bodies of water; (2) Ex- 
tensive and elevated mountain-ranges; (3) Deserts; (4) Forests. The principal 
physiological barriers are : (1) Heat barriers ; (2) Food barriers. 

The power of acclimation ; i. e., of becoming able to live in an environment 
differing widely from that in which the species originated, is possessed to a vary- 
ing degree by different species. Both heredity and variation influence the readi- 
ness with which an animal becomes acclimated. 

When an animal, through dispersal, has reached a new district, a struggle for 
existence begins between the new animal and those it finds in the new country, 
terminating in the survival of the fittest. During this struggle new species 
©ften result. 

All forms of animal life, except man, attain greatest development in tropica] 
regions. 

We distinguish a horizontal and a vertical distribution of animal life. 



SYLLABUS. 329 

A similar cliange is noticed, in the species of animals, in passing from the base 
to the summit of high tropical mountains, as in passing along the surface of the 
earth from the equator to the poles. 

As regards the veitical distribution of life, the fauna of regions between the 
sea-level and 5000 or 7000 feet, resembles, in general, that of the tropics ; between 
the preceding and 15,000 feet, that of the temperate zones. 

The geographic peculiarities of any country have produced a marked influence 
on its fauna. 

The principal realms or regions of animal life are : (1) The Nearctic Eegion; 
(2) The Neotropic Eegion ; (3) The Palsearctic Eegion ; (4) The Ethiopian Ee- 
gion ; (5) The Oriental Eegion ; and (6) The Australian Eegion. 

Some important animals of the Nearctic region are the wolf, fox, grizzly bear, 
polar bear, black bear, beaver, reindeer, and squirrel. Some characteristic birds 
are the bald eagle, horned owl, wild turkey, and grouse. 

Some important animals of the Neotropic region are the flat-nosed monkey, 
blood-sucking bats or vampires, the chinchilla, sloths, armadillos, jaguars, tapirs, 
several varieties of deer, llamas, and alpaccas. Some characteristic birds are the 
humming-birds, trumpeters, macaws, toucans, currasows, trogans, rheas, and con- 
dors. Eeptiles are represented by the boa-constrictor, anaconda, and alligator. 

Some important animals of the Palearctic region are the yak, ibex, chamois, 
camel, bear, deer, elk, reiudeer, beaver, mole, badger, and antelope. 

Some important animals of the Ethiopian region are the lion, leopard, jackal, 
panther, wolf, girafl'e, antelope, gazelle, gnu, spring-bok, zebra, quagga, monkey, 
African elephant, hippopotamus, and rhinoceros. 

Some characteristic birds are the bee-eaters, turacos, hornbills, secretary bird, 
ostrich, and parrot. Some of the reptiles are the puff-adder, rock-boa, python, 
crocodile, and chameleon. 

Some characteristic animals of the Oriental region are the zebu, lion, tiger, 
leopard, panther, fox, the Indian elephant, ape, orang-outang, and gibbon. 
Some characteristic birds are the bulbul, bird of paradise, parrot, and pheasants. 
Some of the reptiles are the python, cobra, vipers, lizards, and crocodile. 

Some important animals of the Australian region are a variety of kangaroos. 
Some characteristic birds are parrots, cockatoos, birds of paradise, lyre birds, 
mound builders, cassowaries, ground-pigeons, and kingfishers. 

Marine fauna are : (1) Littoral, or that of the shallow waters near the coast ; 
(2) Pelagic, or that of the surface waters far from the coasts ; (3) Abyssal, or 
that of the ocean's bottom at all depths. 

Ethnography treats of the varieties of the human race and their distribution. 

Man has a wider range of distribution than any other animal. 

It is generally believed that all the varieties of the human race were originally 
descended from a single species. 

Proofs of the unity of the human race are : (1) The anatomical structure of 
all races is invariably the same ; (2) The gradual modification of types ; (3) 
Folk-lore ; (4) The close resemblance of the language of widely separated races. 



330 PHYSICAL GEOGRAPHY. 

The primary races of man are the Caucasian, the Mongolian, and the African. 

The secondary races are the Australian, the Malay, and the American. 

The Caucasian race comprises: (1) The South Mediterranean Branch, includ- 
ing the Hamitic and Semitic Branches; (2) The North Mediterranean Branch, 
including the Aryan or Indo-European. 

The Hamitic stock of the Caucasian race includes the Berbers, Zouaves 
Kabyles, Tibbus, Copts, Fellaheen, Gallas, and Somalis. 

The Semitic stock includes the modern Arabs, Bedouins, Ethiopians, Israelites, 
and Samaritans. 

The Aryan stock includes the following groups : the Celtic, Italic, Illyric, 
Hellenio, Teutonic, Slavonic, Indo-Irauic, Caucasic, and Uskaric. 

The Mongolian race inhabits nearly all of Asia not occupied by Caucasians. 
It includes : (1) The Sinitic Branch ; (2) The Sibiric Branch. 

The African race inhabits all of Africa and Australia not occupied by Cauca- 
sians, the Malay Archipelago, and the Polynesian Islands. It includes : (1) The 
Negrillo, or Little Negro Branch ; (2) The Negro Branch ; (3) The Negroid 
Branch. 

The Australian race includes the inhabitants of Australia and the Dravidians. 

The Malay race includes: (1) The Malayic branch ; (2) The Negritic branch. 

The American race includes the following groups : The Arctic, North Atlantic, 
North Pacific, Mexican, South Atlantic, and the South Pacific. The American 
race is believed to be a modification of the Mongolian race. 

By far the greater proportion of the metallic ores occur in veins. Veins are : 
(1) Veins of segregation ; (2) Veins of infiltration ; (3) Fissure veins. 

The civilizacion of man is largely dependent on the character of the earth's 
mineral products. 

Mineral substances occur either in the gaseous, the liquid, or the solid state ; 
the last is by far the most common. 

The earth's mineral products may be conveniently grouped under the follow- 
ing classes: (1) Metals and their ores ; (2) Coal, peat, petroleum, natural gas, and 
asphalt ; (3) Clay, kaolin, marl, salt, sulphur, phosphate rocks, and borax ; (4) 
Building stones; (5) The precious stones or gems. 

The most important metals are iron, copper, gold, silver, lead, zinc, aluminium, 
mercury, antimony, nickel, platinum, and tin. 

Iron is the most useful of the metals, and the most widely distributed. Cop- 
per comes next to iron in usefulness. 

The principal natural fuels are coal, peat, coal-oil, and natural gas. 

Clay, kaolin, marl, salt, sulphur, and graphite are extensively employed in 
the arts. 

The principal building stones are granite, gneiss, bluestone, sandstone, mag- 
nesian limestone, marble, and slate. 

The principal precious stones or gems are the diamond, the saupbire, the ruby 
the emerald, the beryl, the topaz, the opal, and the garnet. 



SYLLABUS. 331 



REVIEW QUESTIONS. 

Define zoological geography or zoogeography. Fauna. 

What natural causes led to the dispersal of animals ? Name the barriers that 
opposed this dispersal. 

Distinguish between physiographical and physiological barriers? 

Name some of the most important of each of these barriers. 

What do you understand by the "Survival of the fittest"? How may new 
species of animals sometimes result as a consequence of dispersal ? 

Distinguish between the horizontal and the vertical distribution of ammals. 

Between what limits, in the vertical distribution of animals, does the fauna of 
a tropical mountain-range resemble that of the tropical zone? Of the temperate 
zone? 

State the boundaries of the following animal realms or regions: Nearctic 
Eegion; Neotropic Region; Palsearctic Eegion; Ethiopian Region; Oriental 
Region ; Australian Eegion. 

Enumerate some instances in which the geographic peculiarities of a country 
have exerted a marked influence on its fauna. 

Name some of the characteristic animals of the Nearctic region. Of the 
Neotropic region. Of the Palsearctic region. Of the Ethiopian region. Of the 
Oriental region. Of the Australian region. 

Into what three classes may marine fauna be divided ? State some of the 
peculiarities of each of these classes. 

Define ethnography. 

Which possesses the greater power of acclimation, man or the inferior animals ? 

What arguments can be adduced to show the probable unity of the human 
race? 

Name the primary races. 

Name the secondary races. 

Into what branches may the Caucasian race be divided? 

Name some peoples who have descended from the Aryan stock of the white 
race. From the Semitic stock. From the Hamitic stock. 

Name the parts of the world inhabited by each of the primary and secondary 
races. 

Describe the peculiarities of each of the primary races. Of the secondary. 

Name some of the peoples which belong to each of the various races. 

State what you know of the distribution of minerals. 

In what manner is man's progress dependent on the character and distribution 
of mineral products ? 

How may the earth's mineral products be classified? 

Name any five common metals, and some practical uses to which each ma^ 
be put. 

Name the principal natural fuels. 



332 PHYSICAL QEOORAPHY. 

For what purposes are clays and kaolins employed ? What are marls ? Name 
some of the principal sources of common salt. 

Name the principal building stones. 

What are diamonds ? Where are they found ? How is their value estimated? 
Upon what does it depend ? 

Name some other precious stones. 

MAP QUESTIONS. 

Trace on the map of the Vertical Distribution of Animal Life the character- 
istic fauna in those parts of each of the continents lying between the level 
of the sea and 5000 feet. Between 5000 and 10,000 feet. Between 10,000 and 
15,000 feet. Between 15,000 and 20,000 feet. 

Name from the map of the Distribution of Animals the principal animals of 
the Nearctic region. Of the Neotropic region. The Palsearctic region. The 
Ethiopian region. The Oriental region. The Australian region. 

Name some parts of the world in which the following animals are found 
lion ; elephant ; tiger ; crocodile ; ostrich ; giraffe ; deer ; boa-constrictor ; python 
chamois ; grizzly bear. 

State, from the Ethnographic Map, the portions of the world inhabited by the 
Caucasian race. The Mongolian race. The African race. The Malay race. 
The American race. The x4.ustralian race. 

What different peoples dwell north of the arctic circle ? South of the tropie 
of Capricorn? 

Trace on the map the northern limit of permanent habitation. The southern 
limit. 

Wbat race inhabits Hindostan? What people? What race inhabits Abys- 
sinia? What people? Greenland? Patagonia? China? Mexico? France and 
Spain? Northern Norway and Sweden ? Arabia? Madagascar? 

^Joioo 







Fig. 155a. — Chugwater Ked Beds near Shell, Wyoming. 

PART VI. 

THE PHYSICAL FEATURES OF THE 
UNITED STATES. 



The civilization and development of a country are largely depend- 
ent on its physical features. The soil and the climate exert their 
influence on vegetable and animal life, and these, in turn, react on 
man. If proper soil and climate exist ; if the peculiarities of the 
surface structure permit of ready intercommunication, and if exten- 
sive deposits of coal and valuable metals occur, the future develop- 
ment of the country is assured. 

The physical features of the magnificent domain of the United 
States are such as destine it to play an important part in the civili- 
zation of the future. The peculiarities of its position, its extent, 
the nature of its soil, the climate and rainfall, the size and constancy 
of its navigable rivers, and the extent and variety of its valuable 
mineral deposits, eminently fit it to sustain a very high order of 
civilization. 

333 



334 PHYSICAL GEOGRAPHY. 

CHAPTER I. 

Surface Structure of the United States. 

474. Situation and Extent. — The United States, exclusive of 
its insular possessions and Alaska, occupies the entire breadth of the 
North American Continent, between Lat. 49° N. and 24° 30' N., 
and extends from Long. 66° 50' W. from Greenwich, to 124° 31' W. 
The total area of the United States, exclusive of its insular pos- 
sessions and Alaska, is 3,026,500 square miles. 

475. Coast Line. — The coast line of the United States proper is 
comparatively simple and unbroken. On the east, the Atlantic 
Ocean extends into the land in three wide curves ; on the south, is 
the deep indentation of the Mexican Gulf; on the west, the land 
is thrust out into the Pacific in an almost unbroken curve. The 
total coast line, exclusive of the adjoining islands, is about 12,609 
miles. 

476. Gulfs and Bays. — The principal indentations on the east- 
ern coast are Long Island Sound, Delaware and Chesapeake Bays, 
and Albemarle and Pamlico Sounds. On the western coast are the 
Gulf of Georgia, the fine harbor of the Bay of San Francisco, and 
Puget Sound. 

The Atlantic shores slope gently toward the ocean ; the Pacific 
shores are abrupt. 

477. Islands. — The islands of the Atlantic coast are of three 
distinct classes : those north of Cape Cod are, for the most part, 
rocky, detached portions of the mainland, and are due to the sink- 
ing of the land ; those south of Cape Cod are generally low and 
sandy, and are, for the most part, of fluvio-marine formation ; 
those ofi" the coast of Florida are of mangrove formation. On the 
Pacific coast are the Santa Barbara Islands, a rocky group south' 
west of California ; and Vancouver Island, north-west of Washing- 
ton. 

478. Forms of Relief. — The United States is traversed by two 
distinct mountain-systems : the Pacific Highlands which form a part 



SURFACE STRUCTURE OF THE UNITED STATES. 335 

of the Cordillera of the Rocky Mountains — the predominant sys- 
tem — on the west ; and the Atlantic Highlands, or the Appalachian 
System — the secondary system — on the east. 

479. The Pacific Highlands consists of a broad plateau, tra» 
versed by two distinct mountain systems : the Rocky Mountains, and 
the Pacific mountain-chains. It embraces about one-third of the 
entire territory of the United States proper. 

480, The Rocky Mountains consist of a number of parallel 
chains connected by numerous cross ranges. They rise from the 
summits of an elevated plateau, which in some places is fully 7000 
feet above the sea. The chains are broken in several places by 
transverse valleys or passes, traversed by important rivers. The 
most important of these passes is South Pass, in Wyoming, traversed 
by the Sweet Water River, a tributary of the Platte. The Missouri, 
Rio Grande, and other rivers, flow through similar depressions. 

The chains are separated into northern and southern sections by an elevated 
plateau, over which the Union Pacific Eailroad passes. 

Among the many lofty peaks of this mountain-system are Long's 
Peak, 14,271 feet ; Pike's Peak, 14,108 feet ; Blanca Peak, 14,300 
feet ; Spanish Peaks, 13,620 feet ; and Fremont's Peak, 13,790 feet 
high. 

A remarkable feature of these mountains is the basin-shaped valleys, called 
parks, formed by transverse ranges connecting the parallel ranges. The most 
important of these parks are North, South, and Middle Parks. They are nearly 
rectangular in outline, and are hemmed in by huge mountain-ranges. Each 
park gives rise to an important river. The rich verdure of these deeply sunken 
basins is rendered the more striking by contrast with the desolate mountains 
surrounding them. 

The Yellowstone National Park, in the north-western part of Wyoming, is 
traversed by some of the head-waters of the Yellowstone Eiver. It is a region 
of hot springs, deep gorges, high mountain-peaks, and magnificent scenery. It 
has been set apart by the United States Government as a public park. 

The Great Plains, an elevated plateau, lie along the eastern side 
of the Rocky Mountains. They are undulating plains, which slope 
by almost imperceptible gradations to the valley of the Mississippi. 
They are treeless, and near the base of the mountains have but a 



336 



PHYSICAL GEOORAPHY. 



scanty vegetation. Near the lower part of the slope they merge 
into prairies, covered with a luxuriant growth of grasses. 

481. The Pacific Mountain-chains extend through California, 
Oregon, and Washington, and, in general, are parallel to the Kocky 
Mountains. They comprise the Cascade Mountains in Oregon and 
Washington, and the Sierra Nevada and the Coast Mountains in 
California. 

The loftiest peaks of the Pacific Mountain-chains exceed those 
of the Rocky Mountains in height. The highest peaks are Mt. 

., Rainier in the Cascade 
^ Range, 14,526 feet high; 
Mt. Shasta, 14,380 feet 
high, Mt. Whitney, 14,898 
Mf^^ ^ feet high, and Mt. Brewer, 

13,886 feet high, in the 
Sierra Nevada Range. 

The culminating point 
of the Pacific Mountain- 
chains is Mt. McKinley, 
in Alaska, 20,464 feet 
high. 

The Cascade Mountains 
contain numerous extinct 
volcanoes. 

Tlie Great Basin lies between 
the Wahsatch Mountains on the 
east, and the Sierra Nevada 
and Cascade Eanges on the west. 
It possesses a true inland drain- 
age. East of the Wahsatch 
Mountains, and the western 
flanks of the eleyated peaks 
and ranges of Colorado, lies 
a region drained by the head- 
waters of the Colorado. This 
region, together with the district lying in the middle courses of the river, is 
u wonderful section of country, traversed by streams that have eroded their 




Fig. 156.— The Great Canon of Colorado. 



SURFACE STRUCTURE OF THE UNITED STATES. 337 

valleys and flow through deep canons, some of which are over 6000 feet deep. 
A view of a part of one of the most noted of these canons is shown in Fig. 156. 

482. The Atlantic Highlands, or the Appalachian System, 
extends from Maine to Georgia, nearly parallel to the Atlantic. 
The chain varies in breadth from 150 to 200 miles. The system 
consists of an elevated plateau, bearing several mountain-chains, 
separated by wide valleys. In the northern and southern parts, 
where the elevation is greatest, the system is formed of irregular 
groups, without any definite direction. In the central portions, 
low parallel chains occur separated by fertile valleys. These val- 
leys usually take the names of the rivers which flow through them. 

The system is highest in North Carolina, where Mt. Mitchell, 
6711 feet high, forms its culminating point. 

Beginning on the north, the system includes the White Mountains 
in New Hampshire, with Mount Washington, 6293 feet high ; the 
Green Mountains, in Vermont ; the Adirondacks, in New York, with 
the culminating peak of Mount Marcy, 5344 feet high ; the Catskill 
Mountains, the Blue Mountains, the Alleglianies, the Blue Ridge, 
the Cumberland Mountains, and others. 

483. Great Lo"W Plains. — There are two great low plains in the 
United States : the Atlantic Coast Plain, and the Central Plain, or 
the Plain of the Mississippi Valley. 

The Atlantic Coast Plain lies along the eastern flanks of the 
Appalachian Mountains. It varies in width from 50 to 250 miles. 
Along the coast the soil is comparatively sandy, and has been formed 
by the combined action of the rivers and the ocean. 

Extensive swamps occur in this region— such as Cypress Swamp, in Delaware ; 
Dismal Swamp, north of Albemarle Sound ; Alligator Swamp, between Albemarle 
and Pamlico Sounds ; and Okefinokee Swamp, in Southern Georgia. The Ever= 
glades, in Florida, are the result of coral formation. Farther from the coast 
the plain is more elevated ; long valleys occur, which are very fertile, particu- 
larly near the river bottoms. 

The Plain of the Mississippi Valley lies between the predominant 
and the secondary mountain-systems. It is over 300,000 square 
miles in area, and contains some of the most fertile land in the 
country. 
22 



338 PHYSICAL GEOGRAPHY. 

484:. River-systems. — Oceanic Drainage. — Atlantic System. 

— The United States is particularly noted for the number and 
extent of its navigable rivers. 

Among the important rivers emptying directly into the Atlantic 
Ocean are the Penobscot, Merrimac, Connecticut, Hudson, Delaware, 
Susquehanna, Potomac, Eoanoke, Cajoe Fear, Savannah, Altamaha, 
and the St. John's. 

Of the rivers flowing into the Mexican Gulf, the Chattahoochee, 
Alabama, Mississippi, Sabine, Trinity, Brazos, Colorado, and the 
Rio Grande are the most important. 

The Mississippi, taking its origin in the head-waters of the Missouri — which 
is the true parent stream — is the longest river in the world, its length being 
4490 miles. Its tributaries are, in general, navigable for great distances, and 
thus afford ready communication with different parts of the basin. The impor- 
tant tributaries of the Mississippi on the west are the Minnesota, the Missouri, 
the Arkansas, and the Eed. On the east, are the Wisconsin, the Illinois, and 
the Ohio. 

The Pacific System. — The principal rivers emptying into the 
Pacific Ocean are the Columbia, Sacramento, San Joaquin, and the 
Colorado. 

485. Lake-systems. — The most important lake-system of the 
United States lies in the northern part. It includes, among numer- 
ous others, five of the largest fresh-water lakes in the world: Supe- 
rior, Michigan, Huron, Erie, and Ontario. Their extent is so immense 
that they resemble great inland seas. 

Numerous fluviatile or river lakes occur near the borders of the middle and 
lower courses of the Mississippi and its tributaries. 

486. Inland Drainage. — The rivers and lakes of the Great 
Basin have no outlet to the ocean, and, therefore, form true steppe 
systems. Great Salt and Humboldt lakes are the principal lakes, 
and the Humboldt and the Reese the principal rivers. 

There are two regions in the United States below the mean level of the sea: 

(1) In the southern part of California, in Soda Valley, 200 feet below the sea. 

(2) Death Valley, on the south-eastern border of California, 480 feet below 
the sea-level. These regions are extremely arid. 



METEOROLOGY. 339 

CHAPTER II. 

Meteorology. 

487. Climate. — The United States, exclusive of its insular pos- 
sessions and of Alaska, lies entirely within the limits of the mathe- 
matical north temperate zone. The climate of most of the United 
States, like the climate of the greater part of the central region of 
the temperate zones, is subject to considerable variability. The pas- 
sage of cyclonic and anti-cyclonic disturbances brings with them 
alternate hot and cold waves, changes in the direction of the wind, 
and general weather disturbances. 

Physical Zones. — As regards the actual distribution of heat, 
the United States lies between the annual isothermal lines of 40° 
and 77° Fahr. Its territory, therefore, embraces two zones of phys- 
ical climate : the North Temperate and the Torrid Zones. The 
isotherm of 70°, the boundary of the physical torrid zone, passes 
through Florida, Louisiana, Texas, and Arizona. All the' coun- 
try south of this line lies in the physical torrid zone ; all north of it, 
in the physical north temperate zone. 

The Territory of Alaska lies in the north frigid and north tem- 
perate zones. 

488. Mean Annual Isotherms. — The following peculiarities in the mean 
annual distribution of heat will be seen from a study of the mean annual iso- 
therms on the map {between pages 196-197) : 

The isotherm of 40°, the lowest mean annual temperature shown on the map, 
is found in a few elevated districts in New England, in the elevated districts 
around Lake Superior, and in the higher plateaus of the Eocky Mountains. 

The isotherm of 45°, east of the Mississippi, runs slightly north of the 44° of 
N. Lat., and, except in New York, Vermont, and New Hampshire, extends nearly 
parallel with it. In the Dakotas it bends toward the north-west, reaching the 
northern boundary of the Ur.ited States in Montana, when it bends suddenly 
toward the south-east, until it reaches Central Colorado, where, nearly paralle? 
with its southward deflection, it again turns abruptly to the north. 

In a similar manner the student can trace the other isothermal lines shown 
on the map. 

489. Climatic Contrasts. — There is a marked contrast between 



840 PHYSICAL GEOGRAPHY. 

the climate of the eastern and western coasts of the United States. 
The eastern coast is colder than the western. 

The difference in temperature is greatest in the north ; the mean 
annual temperature of the coast, between Now Jersey and Maine, 
is from 52° to 42° Fahr., while on the shores of Oregon and 
Washington, the mean is nowhere lower than 52°, and in some 
places is much higher. 

In the southern portions of the eastern and western coasts, the con- 
trast is not so decided, owing to the peculiarly cool summers in the 
western part of the continent. 

The Atlantic seaboard is mucli colder than corresponding latitudes on the west- 
ern coasts of Europe. For example, the latitude of New York City is about the 
same as that of Madrid, Naples, and Constantinople ; of Boston, the same as that 
of Rome ; of Portland, Maine, the same as that of Marseilles ; of Quebec, nearly 
that of Paris ; and yet what a striking difiPerence in their climates ! 

The western shores of America are, however, quite as warm as those of Europe. 
Sitka, in Lat. 57°, has a winter mean very nearly the same as that of Edinburgh, 
in the same latitude. 

The higher mean annual temperature of the western coasts over that of the 
eastern may prove of great significance in the future history of the United States, 
since our western shores will admit of cultivation and settlement for a much 
greater distance north than will the eastern. " The difference," says Blodget, 
" covers 12° to 15° of latitude on the coast of the Pacific, and from 5° to 40° on 
the plains east of the Eocky Mountains." 

The great contrast between the climate of the Atlantic and the 
Pacific shores is caused by the direction of the atmospheric and 
the oceanic circulation. In both regions the atmospheric and the 
oceanic circulations are from west to east; hence the higher tem- 
perature of the western shores, which receive the warm, vapor- 
laden winds from the Pacific, a comparatively heavy rainfall, and 
warm ocean currents. The cold Arctic current, which comes down 
the Atlantic seaboard from Baffin Bay, reduces the temperature 
of the eastern coast. 

On the south, the Gulf Stream, emerging from between Florida 
and Cuba, tends to raise the temperature of the southern portions 
of the seaboard. On the Pacific coast, the Japan current, after 
leaving the Asiatic shores, flows southward along the North Amer- 
ican coasts, bathing them with its highly heated waters. 



METEOROLOGY. 341 

490. Constancy of the Climate. — From observations extend- 
ing back as far as the year 1738, it appears that, from that time, the 
climate of the United States has undergone no decided change. 

4.'1. Distribution of Wind and Rain. — The United States, 
exclusive of Alaska and its insular acquisitions, lies in the zone of 
the prevailing westerly winds. Westerly winds, therefore, predominate. 

492. Precipitations. — The rainfall is greatest on the coasts, espe- 
cially on the south and west. On the Pacific coast the rainfall is 
greater on the north, because the winds from the ocean are chilled 
by the high coast ranges. On the Atlantic coast the rainfall is 
greater on the south, owing to the open sweep afibrded the winds 
by the Mexican Gulf and the Mississippi Valley. 

Generally, east of the 100° Long. W. from Greenwich the coun- 
try is well watered, an average of about 40 inches, or 3 J feet, of 
rain falling throughout the year. Between the eastern slopes of 
the Pacific coast ranges and the Rocky Mountains the rainfall is 
scanty, especially on the south, so that agriculture is impossible 
except by irrigation. 

The heaviest annual rainfall is 75 inches, and occurs along the 
Pacific seaboard in Washington and Oregon ; along the Atlantic 
border, it varies from 45 to 50 inches ; near the borders of the 
Gulf States it is about 65 inches ; in the upper half of the Mis- 
sissippi Valley it varies from 25 to 40 inches ; in the lower half, 
from 50 to 60 inches ; in the upper course of the Missouri, from 15 
to 22 inches ; in portions of the Great Basin the rainfall is very 
limited. 

As regards its distribution in time, rain is possible over most of 
the country at all seasons of the year ; over some portions, however, 
it is periodical in character, these districts having a rainy and a dry 
season. 

The rainfall of the greater part of the United States east of the 
Mississippi River is largely dependent on the prevalence of the 
extra-tropical cyclone. Rain may fall, therefore, in this region at 
any time of the year. Near the Atlantic coast, rain is abundant, 
especially in the spring. 



342 PHYSICAL GEOGRAPHY. 

West of the Mississippi the rainfall is irregular. In Wash- 
ington, on the Pacific coast, rain may fall at any time during the 
year. On other parts of the Pacific coast rain is most frequent in 
winter; during the summer it is either scanty or wholly absent. 

493. The Weather Bureau. — Considerable light has been 
thrown on the meteorological conditions of the United States by the 
operations of the " Weather Bureau." 

The Weather Bureau was established by an Act of Congress in 
February, 1870, authorizing the Secretary of War to establish and 
equip stations in different parts of the country, where such simulta- 
neous observations of the meteorological conditions of the atmosphere 
could be taken, as would enable the department to give timely notice 
to all important ports on the Atlantic coast and the Great Lakes, of 
the approach of dangerous storms, and to collect such information 
as would be of value to shipping and other interests. 

In 1890 the direction of the Weather Bureau was, by Act of Congress, taken 
from the War Department and transferred to the Department of Agriculture. 

There are numerous stations established by the Weather Bureau 
in different sections of the United States, where trained and intel- 
ligent observers, several times each day, are required simultaneously 
to make careful observations of the temperature, humidity, and 
pressure of the air, the direction and force of the wind, the clear- 
ness or cloudiness of the sky, and the amount of rain or snow that 
has fallen during a given time. These observations are telegraphed 
to the Central Office at Washington, so that the Bureau is enabled 
to know the actual meteorological conditions which exist throughout 
the country at any given time, and from such knowledge, guided 
by previous experience, to prepare " synopses " of the weather and 
" indications," or forecasts. 

For the preparation of the "indications" the officer in charge prepares a 
number of charts, based on the various data telegraphed to the Central Office, 
as the result of the simultaneous observations at the different stations. These 
charts exhibit the actual meteorological conditions that then exist, those that 
existed during the previous eight hours, and the previous twenty-four hours, 
and the conditions normal for the place at that particular time of the year. The 
data shown on these charts include the temperature, barometric pressure, humid- 



METEOROLOGY. 343 

jty of the air, precipitation, condition of sky, force and direction of wind, etc. 
The "indications" are telegraphed to the press throughout the country. In 
general about 85 per cent, of these indications are verified. 

494. Changes in the "Weather — Passage of a Great Storm. 

— Since nearly all the great storms of the United States are extra- 
tropical cyclones, that move over the country in a general easterly 
direction, it is not difficult, when such a storm begins, to predict 
its general path, and thus foretell coming changes in the weathero 

The principal elements of uncertainty are the exact path in which the storm 
will move over the country and the velocity of such motion. These the Bureau 
can predict, approximately, from a comparison with the iDrevious storms of 
which it has records. 

The whirling motion of the wind, in the Northern Hemisphere, is in the 
opposite direction to that of the hands of a watch. Therefore, as the eastern 
side of a storm approaches any section of country, the winds generally blow 
from the south toward the north. The approach of a storm is usually attended 
by a fall of rain or snow. As the storm moves onward, and its western side 
passes over any locality, the general direction of the wind is from the north 
to the south. Usually after such a storm the weather is cooler. 

Kite Meteorograph. — Observations of the conditions of the 
upper regions of the air, as regards temperature, pressure, humid- 
ity, and wind velocity, have recently been made by means of the 
kite meteorograph, in which self-recording instruments are supported 
in mid-air by means of box kites. 

495. The "Weather and Storm Signals consist of signal-flags 
designed to indicate the probable weather and temperature of the 
coming day, and to give information concerning a coming storm. 

The temperature signal consists of a triangular black flag ; it indicates warmer 
weather when placed above the other flags, and colder weather when placed 
below them. The dear or fair weather signal consists of a square white flag. 
The raiii or snow signal consists of a square blue flag. The cold wave flag consists 
of a square white flag, with a square black centre. The storm signals consist of 
combinations of triangular red, triangular white, and square red flags with black 
centres. The storm signals are displayed at all ports on the Great Lakes or the 
Atlantic seaboard whenever it is considered probable that within twelve hours 
there will be experienced at those ports, or within one hundred miles thereof, 
a wind dangerous to navigation. The information signal, a long triangular red 
flag, is intended to notify ship-masters that, on application to the local observer, 
information will be given them relative to an approaching storm, which it is 



344 PHYSICAL QEOORAPHT. 

thought will be dangerous to vessels about to sail to certain ports. The caution" 
ary signals consist of combinations of triangular red, triangular white, and square 
red flags with white centres ; they are displayed on the Lakes only when the 
winds are expected to be severe, but not dangerous to well-equipped vessels. 

The flags as employed in the weather, storm, and cautionary signals are shown 
on the weather map. 

496. Farmers' Bulletins. — River and Canal Reports. — In 
order to extend the benefits of the " indications " to the agricultural 
districts, farmers' bulletins, containing forecasts, are issued daily. 

To reach the di3"erent cities, towns, villages, and hamlets of the rural districts, 
the indications, or forecasts, are telegraphed every midnight from the Central 
Office to centres of distribution situated in difierent States. These reports 
are at once printed at each of these distributing stations, enclosed in envel- 
opes, and forwarded to every post-office which can be reached by 2 p. M. of the 
next day by the swiftest mail facilities. Great benefit is thus conferred on 
the agricultural interests. 

Warnings of coming floods, movements of river ice, sudden or unusual change 
of level in rivers, are also given when the occasion warrants. The latter warning is 
given whenever the water is likely to rise above a certain level, called the danger line. 

Another series of reports are for the benefit of internal navigation. They 
consist in the announcement, from day to day, of such changes of temperature 
in difierent sections of the country as would be likely either to stop navigation 
by the freezing of the canals, or temporarily to open them sufficiently to enable 
ice-bound vessels to be pressed forward to the termini of the canals. 

The value of the Weather Bureau can scarcely be overestimated ; the saving 
of shipping efi'ected by the timely warning of a single severe storm may more 
than pay the entire expenses of the Bureau for the entire year. We append the 
following resume of the work of the Bureau : 

(1) The announcement of probable weather changes by the publication of 
"indications." 

(2) The timely warning of the approach of severe storms. 

(3) The display of signals indicating coming changes in the weather. 

(4) The i>ublication of farmers' bulletins. 

(5) The river and canal reports. 

(6) The display of symbol-maps, showing the actual state of the weather 
throughout the entire country. 

(7) The publication of daily weather maps, monthly charts, and charts which 
give the results of the observations of years. 

(8) The publication of cotton-region reports, embracing reports of rainfall and 
maximum and minimum temperature throughout the cotton districts from 
April 1 to October 31. 

497. The International "Weather Service. — The success of the 




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METEOROLOGY. 345 

meteorological observations of the U. S. Weather Bureau has led 
to the establishment of stations for simultaneous observations over a 
large portion of the Northern Hemisphere, and some stations in the 
Southern Hemisphere. 

498. Weather Maps. — The actual condition of the weather over the United 
States, on any day, is represented in weather maps published by the Bureau. Two 
of these maps are shown herewith. The upper map shows the meteorological con- 
ditions prevailing on a certain day in April. On that day an area of low barome- 
ter existed in Colorado, Nebraska, and Kansas, within which area the barometer 
was below 29.5 inches, as shown by the isobars, or lines of mean barometric press- 
ure. The country around this area had a gradually increasing barometric press- 
ure, as indicated by the successive isobars 29.6, 29.7, 29.8, 29.9, etc. At the 
same time a storm was moving toward the north-east, as shown by the line of 
crosses. The rate of progress of the storm being known, the Bureau issued the 
following 

Indications. 

" For New England, fair weather followed by light rains to-morrow, north to 
east winds, slight rise in temperature. 

For the Middle Atlantic States, increasing cloudiness and rain, winds shifting 
to east and south, slightly warmer weather, lower barometer. 

For the South Atlantic States, local rains, warmer, partly cloudy weather, 
south-east to south-west winds, lower barometer. 

For the East Gulf States, threatening 'weather and rain, followed by clearing 
weather, southerly to westerly winds, slight rise in temperature, followed in west 
portion by a slight fall in temperature. 

For the West Gidf States, local rains, followed by clearing weather, winds 
shifting to west and north, nearly stationary, followed by lower temperature, 
and rising barometer to-morrow. 

For Tennessee and the Ohio Valley, cloudy weather and rain, southerly to west- 
erly winds, rising temperature, falling barometer and severe local storms, fol- 
lowed to-morrow in west portion by cooler weather and higher barometer. 

For the Lower Lake Region, threatening weather and rain, east to south winds, 
lower barometer, and rising temperature. 

For the Upper Lake Region, threatening weather, with rain or snow, north- 
easterly winds becoming variable, falling, followed by rising barometer, slight 
rise, followed by falling temperature. 

For the Upper 3Iississippi Valley, threatening weather and rain, severe local 
storms, winds shifting to west and north, followed by higher barometer and 
colder weather. 

For the Missouri Valley, rain or snow, generally colder, cloudy, followed by 
partly cloudy weather, dangerous local storms in southern portion, winds shifting 
to north and west, with colder weather and higher barometer. 

Light rains are indicated to-morrow for New England and the Middle Atlantic 



346 PHYSICAL GEOGBAPHY. 

States with warmer weather. Clearing and fair weather is indicated for the "West 
Gulf States and thence northward over the Upper Mississippi and Missouri Val- 
leys, and the Lake Eegion. 

The Ohio Eiver, Cumberland, Tennessee, and the Mississippi at St. Louis, 
Cairo, Vicksburg. and New Orleans, will continue slowly falling. 

Cautionary signals continue at Milwaukee, Chicago, Grand Haven, Detroit, 
Toledo, Sandusky, Cleveland, Erie, and Buffalo." 

The lower map shows the actual conditions of the weather on the following 
day. The area of low barometer, or storm-centre, has moved eastward and the 
storm is now central over Western Pennsylvania and the adjoining States. The 
actual condition of the weather, showing the correctness of the predictions, will 
be seen from an inspection of the following synopsis issued by the Bureau. 

Synopsis for the Past Twenty-fovir Hours. 

" The severe storm which was central in the Lower Missouri Valley yesterday 
morning moved directly east, causing dangerous gales on the Lakes and general 
rains in the Southern States, the Middle States, and the Ohio Valley. Snow and 
rain continue in the Lake Eegion this morning. Threatening weather is reported 
from New England, and colder, fair weather from the north-west and south-west. 
The temperature has fallen about 10° in the Mississippi, Ohio, and Missouri Val- 
leys and Upper Lake Eegion, with north to west winds ; and it has risen slightly 
in the districts on the Atlantic coast, with north-easterly winds in New England 
and on the Middle Atlantic coast, and south-westerly winds in the South Atlantic 
States. The barometer is unusually low near Pittsburg, and it is highest in 
Nebraska. A light norther prevails on the Texas coast." 



►ojd^c 



CHAPTER III. 

Vegetable and Animal Life. 

499. Vegetation. — The distribution of vegetation throughout the 
United States accords with the distribution of the rainfall. Four 
characteristic plant regions are found : the Forest, the Prairie, the 
Steppe, and the Pacific Eegion. 

500. The Forest Region. — The chief requisite of forest growth 
— an abundant rainfall, well distributed throughout the year or dur- 
ing the time the trees are growing — is found, especially in the coun- 
try east of the Mississippi, where luxuriant forests exist, except 
where removed by civilization. 

The pine, spruce, hemlock, fir, larch, juniper, and deciduous trees. 



VEGETABLE AND ANIMAL LIFE. 



347 



such as the oak, hickory, chestnut, locust, beech, maple, birch, alder, 
and poplar, are common in the North. 

Deciduous trees characterize the middle portions of the forest 
region. In the number 
and variety of its spe- 
cies the oak is pecu- 
liarly characteristic of 
the middle part of the 
forest region. In the 
southern portion of the 
forest region evergreen 
trees, such as the live- 
oak and the magnolia, 
are characteristic. 

The forests have been 
removed, over extended 
areas, from all three 
parts of the forest re- 
gion. The cut logs, 
when the river-courses 
are sufficiently large, 
are transported to dif- 
ferent sections of the 
country in huge rafts. 

501. The Prairie 
Region. — West of the Mississippi Valley, to the Plateau of the 
Great Plains, the comparatively scanty rainfall produces extensive 
prairies, covered with grasses and flowering herbs. Forests are want- 
ing, except along the river-courses. 

502. The Steppe Region. — From the western limits of the 
Great Plains to the Sierra Nevada and Cascade ranges, lie the ele- 
vated plateaus of the predominant mountain-system. Here the 
rainfall is irregular and scanty, and the vegetation presents the 
peculiarities of a true steppe. But few species of plants occur ; the 
cactus and wild sage are characteristic. 





ilii 


^^-s'^ifeS?^ {'-•'^"- '^"^ 





Fig. 157.— Mammotli Trees of California. 



348 PHYSICAL QEOOBAFHY. 

503. The Pacific Region. — From the western limits of the 
Steppe region to the Pacific coast lies a region whose features, in 
some respects, resemble those of the forest region. In Washington 
and Oregon dense forests of fir and spruce trees occur. The cedar, 
larch, maple, oak, and chestnut are common. In California the 
periodical rainfall nearly excludes the forest from the valleys and 
plains ; but on the mountain-slopes, where rains are more frequent, 
forests abound. The pine, fir, and oak are characteristic. 

On the slopes of the Coast Mountains and the Sierra Nevada and Cascade 
Eanges, dense forests of pine and fir trees are found. In some parts of these 
regions the trees frequently attain an immense size, many of them exceeding 300 
feet in height. The largest are the celebrated "Mammoth trees of California," 
a species of pine. Some of these trees are 350 feet high, and have a circumfer- 
ence of 110 feet at the base. In some of the fallen trees, the hollow, decayed 
trunks readily permit the passage through them of a man and horse. 

504. Animal Life. — The large animals now found in the United 
States are principally those which have been domesticated, such as 
the horse, cow, sheep, mule, goat, and dog. 

In some of the sparsely settled regions of the East, and over large 
areas in the West, a few wild animals are yet to be found. In parts 
of the Appalachian system the black bear, panther, and deer are 
found. The moose is found in the northern parts of the United 
States. The immense herds of buffalo that once roved over the 
plains west of the Mississippi are practically extinct, having been 
replaced by herds of domestic cattle. The grizzly bear, the wolf, 
the mountain sheep, and the mountain goat are found on the moun- 
tains of the Pacific slope. 

In the South, the warm, sluggish waters of the lower courses of the 
rivers and swamps harbor numerous alligators. 

A number of species of serpents occur, but only two, the rattle- 
snake and the copperhead, are venomous. 

The manatee, or sea-cow, a curious herbivorous animal with paddle- 
like legs, found in the shallow waters of the coast of Florida, some- 
times attains a length of ten feet. 

Some species of the manatee in the North Pacific, off Alaska, reach thirty 
feet in length. 



AQRICULTUBAL AND MINERAL PRODUCTIONS. 349 



CHAPTER IV. 

Agricultural and Mineral Productions. 

505. Agricultural Productions. — The principal agricultural 
productions of the United States are wheat, corn, rye, oats, barley, 
buckwheat, hay, hops, potatoes, flax, tobacco, rice, cotton, and sugar. 

506. The Cereals, wheat, corn, rye, oats, barley, and buckwheat, 
are grown principally north of 36° N. Lat. According to the census 
of 1900, the States giving the largest yield of corn were Iowa, 
Illinois, Nebraska, and Missouri, while those yielding the most wheat 
were Kansas, Minnesota, California, Washington, and Nebraska. 

The yield of corn is greater than that of any other cereal ; the corn-crop of the 
year 1906, in the United States, amounted to 2,927,416,091 bushels. The wheat- 
crop of 1906 amounted to 735,260,970 bushels. 

507. Tobacco and Flax are raised in large quantities in various 

sections of the country. 

The principal tobacco- 
producing States are Ken- 
tucky, Virginia, North 
Carolina, Tennessee, 
Pennsylvania, and Wis- 
consin. 

The entire yield of tobacco 
in 1906 was 682,428,560 pounds. 

The principal flax-pro- 
ducing States are Minne- 
sota, Iowa, South Dakota, 
and Nebraska. 

The total value of flax-pro- 
ducts in 1906 was $14,283,164. 

508. Cotton, Rice, and Sugar are cultivated mainly south of 
36° N. Lat. 

The principal cotton -producing States are Texas, Mississippi, Ala- 
bama, South Carolina, Georgia, Arkansas, and Louisiana. 




Fig. 158.— Tobacco Field. 



350 



PHYSICAL OEOGBAPHY. 



The cotton-crop of the year 1906, in the United States, amounted to 1], 368.424 
bales, of an average net weight of 487 pounds per bale. 




Fig:. 159.— Cotton Field. 



509. The principal rice-producing States are South Carolina, 
Louisiana, Georgia, and North Carolina. The rice-fields are con- 
fined to low, flat, marshy tracts along the rivers or near the coast. 

The yield of rice in 1906 was 
495,985,800 pounds. 







Fig. 160.— Cutting Sugar-cane. 



The principal sugar-pro- 
ducing State is Louisiana, 
the plantations being con- 
fined mainly to the rich 
lands in the neighborhood 
of the Mississippi Delta. 
Sugar is grown also in 
South Carolina, Tennessee, 
and Texas. 

The total production of cane- 



sugar in 1906 amounted to 514,820,000 pounds. 

Beet-sugar is produced in several of the States, principally in California, 
entire production in 1906 was 967,223,040 pounds. 



The 



AGRICULTURAL AND MINERAL PRODUCTIONS. 351 

Maple-sugar is produced in most of the Northern States, principally in Ver- 
mont. The total production in 1906 amounted to 41,928,770 pounds. 

510. Mineral Productions. — The United States is noted for the 
richness and variety of its mineral deposits. Nearly all the impor- 
tant metals are found in various portions of the country, some of the 
deposits extending over areas of great extent. 

511. Mineral Products of the United States. — The following 
table, taken from the United States Geological Survey, shows the 
different mineral products of the United States for the year 1899, 
arranged in the order of their values : 

Pig iron $245,172,654 

Bituminous coal 167,935,304 

Copper 104,190,898 

Pennsylvania anthracite 88,142,130 

Gold (coining value) 71,053,400 

Silver (coining value) 70,806,626 

Petroleum 64,603,904 

Building stone 44,736,576 

Natural gas ... 20,024,873 

Lead 18,831,600 

Cement - , , . , . 14,417,058 

Zinc 13,731,920 

Brick clay 11,250,000 

Salt ■. . 7,509,184 

Mineral waters 6,948,030 

Phosphate rock , 5,084,076 

Limestone for flux 4,695,205 

Zinc white 3,211,680 

Aluminium 1,716,000 

Mercury 1,452,745 

Gypsum 1,287,080 

Borax - 1,139,882 

Clay, other than for bricks 1,250,000 

Mineral paints 728,389 

Asphaltum 553,904 

Antimony 251,875 

Flint 231,345 

Feldspar 228,545 

Precious stones 185,770 

Barytes 139,928 

Bauxite 125,598 

Bromine 108,251 

Sulphur 107,500 



352 PHYSICAL OEOOBAPHY. 

From the foregoing table it will be seen that pig iron leads all the 
other mineral products in its money value. Bituminous or soft coal 
comes next ; then follow copper, anthracite or hard coal, gold, silver, 
petroleum, building stone, natural gas, and lead. These substances, 
the first ten on the list, possess jointly a value in excess of all the 
other mineral products. 

512. Metallic Substances. — The principal metals produced in 
the United States, in the year 1906, named in the order of their 
money values, are iron, copper, gold, silver, lead, zinc, aluminium, 
and mercury. 

Iron. — Valuable ore deposits occur in the States bordering on 
Lake Superior, especially in Michigan ; in New York State near 
the Adirondack region ; in Pennsylvania, Missouri, Alabama, and 
elsewhere. 

Pyrites, a common ore of iron, consisting of iron combined 
with sulphur, is employed in the production of sulphuric acid. 
Sulphuric acid is produced in great quantities in Kansas. 

The United States leads the world in the production of iron. 
Pig iron is the rough form of iron first produced from the ore. 

Copper comes next to iron in the money value of the output. 
It occurs in large deposits either in a pure or native state, or com- 
bined with other ores, in Montana, in Michigan near the shore of 
Lake Michigan, in Arizona, Utah, New Mexico, and California. 

Gold stands third in the money value of the output. Valuable 
deposits occur at Cripple Creek and other localities in Colorado, 
in California, Montana, Idaho, Washington, Oregon, Arizona, New 
Mexico, and Alaska. The United States has led the world in the 
production of gold during the last few years. 

Silver occurs in a pure or native state in the Lake Superior 
copper districts, or associated with the gold deposits in the gold 
fields already mentioned, or associated with lead sulphide or 
galena. 

Lead and zinc occur in large deposits, mainly as sulphide of lead 
or galena, and as sulphide of zinc or jach in various parts of the 
country. The greatest deposits are found in Kansas and Missouri 



AGRICULTURAL AND MINERAL PRODUCTIONS. 353 



Aluminium is produced from various ores by electrical means 
in fairly large quantities at Niagara Falls. 

Mercury is produced from the deposits in California, Texas, and 
Oregon. These States are named in the order of the value of 
their output. 

513. Non-metallic Substances. — Among the more important 
non-metallic substances are bituminous coal, anthracite coal, petro- 
leum, stone, natural 

gas, cement, brick 
clay, salt, mineral 
waters, phosphate 
rock, limestone for 
flux, gypsum, borax, 
asphalt, flint, feldspar, 
and sulphur. These 
substances are named 
in the order of the 
money value of their 
production during 
1906. 

Coal. — The coal- 
fields of the United 
States are the richest 
in the world, this 
country now leading the world in the value of this product. The 
principal anthracite fields are those of' Pennsylvania. The prin- 
cipal deposits of bituminous or soft coal occur in the following 
States, which are named in the order of their output for 1906 ; 
viz., Pennsylvania, Illinois, Ohio, West Virginia, Alabama, Colorado, 
Kentucky, Iowa, Wyoming, Kansas, Tennessee. 

The principal States producing coke, named in the order of 
their output, are : Pennsylvania, West Virginia, Alabama, and 
Virginia. 

514. Petroleum, Natural Gas, and Asphalt. — The petroleum 
and natural gas fields in the United States are exceedingly valuable, 

23 




Fig. 161.— Coal Mine, Culm Pile, and Breaker. 



354 



PHYSICAL GEOGRAPHY. 



the value of the output for 1906 reaching a total of over $84,000,000. 
The value of the output of asphalt was much less. 

The principal oil fields in the Appalachian district are found in 
Pennsylvania, West Virginia, and Ohio. 
Valuable fields also occur in Texas, In- 
diana, Kansas, California, and Wyoming. 

At Beaumont, Texas, oil has recently 
been discovered, and great " gushers " pro- 
duce immense quantities of oil. For most 
commercial uses it is necessary to refine or 
purify the oil. 

The principal gas fields in the United 
States are fouud in Western Pennsylvania, 
Ohio, Indiana, and Kansas. 

The gas is obtained by borings similar to 
those made for artesian wells or coal-oil wells. 
From the gas wells thus formed the gas issues 
forth with great velocity. When lighted, it 
burns with a flame somewhat similar to that 
of ordinary illuminating gas. Like ordinary 
gas it burns with a pale bluish flame when 
mixed with air, and afibrds an excellent 
source of artificial heat. 



1^/m^ 



Natural gas has been known for many years past, 
but it is only since about 1880 that its great extent 
and quantity have been ascertained. In niany dis- 
tricts natural gas has almost entirely replaced ordi- 
nary coal as a source of heat. The value of such a 
natural product in any manufacturing centre can 
scarcely be overestimated, and its use in any local- 
ity has in all cases been attended with a great 
increase in the extent and variety of its manufac- 
tures. Such deposits, however, in a comparatively short time, must become 
exhausted. 

The gas escapes from the well under great pressure. Before its delivery to 
consumers, through pipes like ordinary gas-pipes, the pressure is reduced by 
suitable contrivances ; so that its consumption is not attended with any greater 
risk than that attending ordinary illuminating gas. 



Fig. 162.-011 Well or 
" Gusher " at Beaumont, 
Texas. 



ALASKA. 355 

515. Salt. — Beds of rock-salt occur in Louisiana, Virginia, and 
in various parts of the West. Large quantities of salt are obtained 
by evaporating the waters of saline or brine springs, which are of com- 
mon occurrence. The most valuable are found in New York, in the 
neighborhood of Salina and Syracuse ; in Virginia, Michigan, Ken- 
tucky, and in the Far West. 

516. Building Stones. — Large deposits of valuable building 
stones are found in all parts of the country. Among the most com- 
mon are various kinds of sandstone, marble, granite, slate, magnesian 
limestone, serpentine, gneiss, and mica schist. Valuable deposits of 
clay occur, from which excellent bricks are made. 



CHAPTER V. 

Alaska. 

517 Extent of Territory. — The Territory of Alaska, a part of 
the domain of the United States, embraces the nortla-western part 
of the North American Continent, and extends south, from the shores 
of the Arctic Ocean to about 54° IST. Lat. The main part of the 
Territory lies west of the 141° W. Long, from Greenwich. South of 
Mt. St. Elias it embraces a narrow strip extending southeastwardly 
along the coast of British Columbia. Its greatest north and south 
extent is about 1100 miles, and its greatest east and west extent 
about 800 miles. 

The Territory of Alaska embraces an area of about 580,107 square 
miles, or, approximately, about one-fifth of the whole area of the 
remainder of the continental domain of the United States. This 
country was purchased from Russia by the United States in 1867, 
at a cost of $7,200,000. 

Indentations of the Coast.— The coast-line of Alaska is ex- 
ceedingly irregular, its entire length amounting to 8000 miles. The 
shores bordering on the Arctic Ocean are the least indented. The 
western and southern coasts are deeply indented. 



356 PHYSICAL GEOGRAPHY. 

Bering" Sea and Straits separate Alaska from Asia. The Pacific 
Ocean enters the wide curve of the southern coast as the Gulf of 
Alaska. Smaller indentations on the western coasts are found in 
Bristol Bay, Kuskokwim Bay, Norton Sound, Kotzebue Sound, and 
in the numerous bays and inlets on the southern coasts, in which 
true fiords occur. 

518. Islands. — Numerous islands lie ofi* the western and south- 
ern coasts. The principal of these are St. Lawrence, Nunivak, 
and the Pribylofi" Islands in Bering Sea, on the western coast ; the 
Aleutian Islands, which extend in a curve from the Alaskan Penin- 
sula nearly to Kamtchatka ; Kadiak Islands, off the southern shores 
of the peninsula ; and the Alexander Archipelago, off the south- 
eastern shores, containing, among some 1100 islands, Baranofi"; Chi- 
chagof, Kupreanof, and Prince of Wales Islands. 

519. Surface Structure. — The northern portions of Alaska are 
low and flat, and the plains, drained by a few small, sluggish .streams, 
are, for the most part, frozen moor-lands, similar to the tundras of 
Northern Siberia. They form a dreary, desolate country, for the 
greater part unexplored, covered during the brief summer by a com- 
paratively dense growth of grasses. 

The rest of Alaska is generally mountainous, being traversed by 
prolongations of the Pacific Mountain-system. The highest eleva- 
tions are Mt. McKinley, rising 20,464 feet above the level of the sea ; 
Mt. St. Elias is 19,500 feet high. The mountains of Alaska contain 
numerous glaciers which descend to the level of the sea. The 
chain of the Aleutian Islands is mountainous, and, like the moun- 
tains of the south-western coast, contains many volcanic peaks. 
The islands of the Alexander Archipelago and the adjoining coast 
are of the fiord formation, the coasts being indented by deep and 
relatively narrow water-ways. Glacier Bay, one of these indenta- 
tions on the mainland north of Chickakoff Island, receives numer- 
ous glaciers descending from mountains in the St. Elias range. 

520. Drainage System. — The principal river of Alaska is the 
Yukon, which, so far as known, has a length of about 2000 miles. 
It is one of the largest rivers in North A merica, so far as the volume 



ALASKA. 357 

of its discharge is concerned, wLich appears to be as great as that of 
the Mississippi. In some portions of its lower course it is, in places, 
20 miles wide. An extensive delta formation at its mouth shuts 
off navigation for all large vessels. The Koyubuk and the White 
are its principal tributaries. 

The Kuskokwim is the only other important river. Unlike the 
delta-mouth of the Yukon, the Kuskokwim discharges its waters into 
Bering Sea through a wide estuary. The spring tides sometimes 
rise in this estuary to the height of over 50 feet. 

The glaciers of the south-eastern coast feed a number of lakes, so 
near together as to permit the establishment of portage-routes of 
travel. 

521. Climate. — The climate of Alaska is, genei'ally, cold and wet, 
although the influence of the Japan Current, and the westerly winds 
and rain, render the mean annual temperature much warmer than 
corresponding latitudes in the interior, or even on the eastern coasts 
of the North Arrerican Continent. Fogs and rains are frequent. 
The annual rainfall at Sitka, on Baranoff Island, varies from 60 to 
85 inches. The mean annual temperature is about 42°. 

522. Vegetation. — Dense grasses cover portions of the tundras, 
river valleys, and hillsides during the brief summer. The wet cli- 
mate renders the curing of hay a difficult matter, consequently the 
rearing of cattle is attended with difiiculty. 

Portions of the lower mountainous slopes and river valleys are 
covered with forests of cedar and spruce. In the greater part of 
the Territory no timber grows at an altitude greater than 1000 
feet above the sea. Turnips, potatoes, and radishes are cultivated 
■with fair success in southern portions of the Territory. 

523. Animal Life. — The rivers are visited by myriads of salmon 
during the breeding season. This fish forms the principal food of 
the inhabitants, who, at the beginning of the season, desert the 
interior for the banks of the rivers. Halibut, herring, codfish, and 
mackerel are caught off the coasts of the Territory. 

The fur seal and the sea-otter are the principal valuable fur- 
bearing animals. The Pribyloff Islands in Bering Sea are the 



358 PHYSICAL GEOGRAPHY. 

principal breeding-grounds of the fur seals. The walrus is killed 
by the natives for its flesh, oil, hide, and tusks. The whale is found 
in the Arctic waters of the northern coast. The polar bear, the 
brown bear, the mink, the black or silver fox, the moose, and the 
caribou are also found in the Territory. Dense swarms of blood- 
thirsty mosquitoes and black flies occur in nearly all parts of the 
country. 

524. Minerals, — Beds of coal of an inferior quality have been 
discovered in various parts of the country. Extremely valuable 
gold deposits, both as placers and in quartz veins, occur near Cape 
Nome, in northwestern Alaska, near the entrance of Norton Sound ; 
in the neighborhood of the Klondike region near the Yukon River, 
west of Dawson ; on the islands of the Alexander Archipelago ; 
on the neighboring mainland, and elsewhere. Deposits of silver, 
copper, iron, and lead also occur. 

525. Inhabitants. — The inhabitants of Alaska consist chiefly 
of the Esquimaux or Innuit, the Indians, the Aleuts or Inhabitants 
of the Aleutian Islands, the Creoles or Russian Half-breeds, and 
the inhabitants of the remaining archipelagoes, together with a 
constantly increasing Caucasian or white population attracted by 
the extensive gold deposits. 

Sitka, on Baranofi" Island, is the principal settlement. 



CHAPTER VI. 
The Insular Possessions of the United States. 

526. Enumeration. — The recently acquired insular possessions 
of the United States are the Philippine Islands, the Hawaiian or 
Sandwich Islands, the island of Porto Rico, the island of Guam, 
in the Marianne GroujD, and the island of Tutuila, in the Samoan 
Group, and Wake Island, in the mid-Pacific Ocean. 

527. The Philippines. — The Philippine Islands lie off the east- 
ern coast of Asia in the Pacific Ocean, approximately, between 



THE INSULAR POSSESSIONS OF THE UNITED STATES. 359 



125 




FORMOSA 

MAP OF THE 

'SoutHCa,, PHILIPPINE 

BOTOt. TOBAGO I, ISLANDS 



BASHEE CHANNEL 

^ASHEE ISLANDS a 
BATAN ISLANDS S 



^ 



INTANG CHANNEL \ 

e CLARO BABUYAN 
lALAYAN I ca 
f^UPlRll a'=' BABUYAN ISLANDS 

gOAMIGUIN I 
teadofp ^Pt Pata , 



^ 



Scale of Miles 







> l1 / EURIAS l\ ^--7 ^IS>.'^ 



Palapa 






^ LIRAN I <sS »o 






"IsjjRlGAO I 

O It £alanffonan_,^^ f~ S 'J -'S '- "^^ '^ 

o T? ^ f'n 1 ^ivilNDANAO^ 

Zamboan^f^'"'" '^C ^ I" ' ?, S / 

A ^^Basilan Strait \} ' i ~\ ^ 

RAN IS. _ 'V^J'S-'SILAN 

6 6 .•• ,0 

suLu i.,iss:?'-' ^c> 



C -^ E L E BE S 




Ti y ^^Augustln 

Serangani Jjag\J 

Serangani Pt. ^ 



s i; J. 



n 



Longitude East from Greenwich 125 



360 



PHYSICAL GEOORAPHT. 



Long. 116° and 127° E. from Greenwich, and Lat. 5° and 20° N. 
They are, consequently, situated entirely within the tropics. They 
are south-east of China and east of Anara, from which they are 
separated by the South China Sea. They comprise about 2000 
islands, with a combined land area estimated at 140,000 square 
miles. Luzon, the largest island, lies near the northern end of the 
group, and has an area about equal to that of the State of Ohio. 
Mindanao, the next largest island, has an area somewhat less. 
Samar, Panay, Palawan, and Mindoro have each an area, approxi- 
mately, equal to the State of Connecticut. Leyte, Negros, Cebu, 
Masbate, and Bohol are other fairly large islands. The coast line 
of the principal islands is, approximately, 11,000 miles. Manila, 
situated on Manila Bay, in the island of Luzon, is the principal 
city of the Philippine Islands. 




Fig. 163.— Native Houses, Philippine Islands. 

528. Agricultural Products. — Animals. — The principal agri 
•cultural products are rice, corn. hem.p, sugar, tobacco, cocoanuts 



THE INSULAR POSSESSIONS OF THE UNITED STATES. 361 



and cacao. Yams, bananas, and pineapples are also raised. Only 
about one-ninth of the area is under cultivation. The rice and 
corn are principally produced in Luzon and Mindoro. Hemp is 
produced in southern Luzon, Mindoro, and Mindanao. Tobacco 
is raised in nearly all the islands, but the best and largest crops 
are those of Luzon. Sugar is raised in most of the islands south of 
Luzon. Cocoanuts are grown in southern Luzon. Cacao is raised 
in the southern islands. Cattle, sheep, and goats have been intro- 
duced into the archipelago. Pigs and chickens are common. The 
carabao or water buffalo is the principal beast of burden. 

The native houses are constructed largely of bamboo, which forms 
the framework. The floors are covered with split bamboo poles 




Fig. 164.— Bamboo Lumber-yard in tbe Philippines. 

placed with the rounded side upward. The lowest floor, which is 
entered by means of a bamboo ladder, is several feet above the 
ground. 

529. Minerals and Forests. — Undeveloped deposits of coal or 
lignite, petroleum, copper, iron, and lead are said to exist. Gold is 
mined to some extent in Luzon. 



362 



PHYSICAL GEOGRAPHY, 



Dense forests cover large areas of all the islands, and in them are 
found many species of trees which furnish valuable hard woods. 
Sapan wood, from which a dye is extracted, known as "false crim- 
son," to distinguish it from cochineal, cedar, bancal, and ebony are 
some of the woods. The bamboo, a tree-like variety of grass that 
often attains a height of 50 feet or over, is native to different parts 
of the archipelago. It is noted for the wonderful rapidity of its 
growth. The bamboo poles constitute the principal woods of the 
native lumber yards. Not only does this wood enter largely into 

the construction of the 
native houses, but it is 
employed also for the 
masts of small ships, 
in the construction of 
the native boats, and for 
agricultural and house- 
hold implements, etc. 

There are numerous 
excellent harbors in the 
archipelago. 

530. Climate.— The 
climate is hot, especially 
in the southern portion of the group. The excessive moisture often 
renders the heat very oppressive. 

The south-west monsoon, which begins in May, brings heavy 
rains, which continue until October. The heaviest rainfall occurs 
during July and August. During the prevalence of the north-east 
monsoon, which occurs between October and May, the weather is 
comparatively dry. The annual rainfall, in some parts of the 
islands, is as high as 114 inches. 

Luzon, and the islands in its vicinity, are subject to severe 
typhoons. The region is one of active volcanoes, and is subject 
to severe earthquake shocks. Mayon, near the southern end of 
Luzon, 8925 feet high, is one of the most famous volcanoes in the 




Fig. 165.— Volcano of Mayon, Philippine Islands. 



THE INSULAR POSSESSIONS OF TEE UNITED STATES. 363 




Rice Fields of Hawaii. 



archipelago. It is almost constantly in action. Taal, on the island 
of Luzon, and Apo, on Mindanao, are also important volcanoes. 

531. The Hawaiian or Sandwich Islands are situated in 
the Pacific Ocean, approximately between Long. 154° W. and 
161° W., and from 19° to 
22° N. Lat. The princi- 
pal islands lie south of the 
Tropic of Cancer, and are, 
therefore, situated within 
the tropics. 

Hawaii, at the southern 
end of the group, is the 
largest island. Maui, Oahu, 
Kauai, Molokai, and Lanai 
are next in importance. 
The total land area is about 
6740 square miles. The principal city is Honolulu, on the island 
of Oahu. Its situation, in relation to the sailing routes between the 
principal ports of the Pacific, has given it the name of " The Cross- 
roads of the Pacific." 

532. Surface Structure. — The Hawaiian Islands are of volcanic 
origin, and are, therefore, mountainous. Hawaii is formed mainly 
of three great volcanic cones: Mt. Kea, 13,805 feet, now extinct; 
Mt. Hualalai, in eruption in 1801, 8275 feet, and Mauna Loa, 13,675 
feet, in frequent eruption. Kilauea, a well-known active volcano, is 
a crater on the eastern slopes of Mauna Loa. 

533. Climate. — Rainfall. — On the coasts tropical climates exist. 
The mean annual temperature of Honolulu for the daytime is 80° F. 
On the mountain slopes, the usual decrease in temperature with 
increased elevation occurs. 

The rainfall on the slopes toward the prevailing wind is copious, 
especially at fairly considerable elevations. At altitudes of 900 
feet the annual rainfall is 116 inches, and at 2800 feet, 179 inches. 

534. Ftoductions. — The soil is of volcanic origin. The princi- 
pal agricultural products are sugar and cofiee. Tropical fruits, such 



364 



PHYSICAL QEOGBAPHT. 




as bananas and pine-ap- 
ples, are grown in large 
quantities ; oranges, limes, 
lemons, and rice are also 
grown. 
The sugar crop is especially 
vs luable. The rice fields are 
worked almost entirely by the 
Chinese. 
Extensive forest areas exist. 
535. Porto Rico is the most eastern 
and the smallest of the Greater Antilles 
of the West Indies. It is situated about 
60 miles east of the island of Hayti, be- 
tween Long. 65° 15' W. and 67° 15' W. 
from Greenwich, and 17° 50' and 18° 45' 
N. Lat. It is, therefore, a tropical island. 
Its approximate area is 3670 miles. It 
is a mountainous country, high in the 
centre and low near the coasts. 



SYLLABUS. 365 

536. Climate and Products. — The heavy rainfall has eroded the 
mountains so that, from the ocean, they present a deeply cut, ser- 
rated appearance. 

The soil is extremely fertile. The principal agricultural products 
are sugar, coffee, tobacco, cotton, maize, and rice. There is also pro- 
duced a great variety of tropical fruits, such as bananas, pineapples, 
mangoes, grape fruit, oranges, and lemons. 

Valuable forests, containing a great variety of trees, cover much 
of the mountainous country. 

The island has valuable mineral deposits. 

537. Guam, the principal island of the Ladrone or Marianne 
Group, was ceded by Spain to the United States, December 10, 
1898. Guam is situated in the Pacific Ocean, north-east of the 
Philippines, about 5200 miles from San Francisco, and 900 miles 
from Manila ; it has a length of about 32 miles and a circumference 
of 100 miles. 

538. Tutuila, one of the Samoan Islands, is situated in the 
tropical Pacific Ocean, south of the equator, some 4000 miles from 
San Francisco, 2200 miles from Hawaii, and 4200 miles from Manila, 
It has an area of about 54 square miles, and contains the magnifi- 
cent harbor of Pago-Pago, sufficiently large to more than accommo- 
date the entire navy of the United States. 

539. Wake Island, a lonely island in the mid-Pacific, is 1300 
miles east of Guam, and 2000 miles west of Honolulu. It has a 
good harbor. 

*o>©^o« 

SYLLABUS. 

The United States of America, exclusive of Alaska and its insular possession, 
covers an area of 3,026,500 square miles. 

The coast line is comparatively simple and unbroken. The principal indenta- 
tions on the east are Long Island Sound, Delaware and Chesapeake Bays, and 
Albemarle and Pamlico Sounds ; on the west, the Gulf of Georgia, the Bay of 
San Francisco, and Puget Sound. 

The slope of the Atlantic shores is gradual, whereas that of the Pacific shores 
fe abrupt. 



366 PHYSICAL GEOGRAPHY. 

On the Atlantic coast, tlie islands north of Cape Cod are, for the most part, 
rocky ; while those on the south are generally low and sandy. 

Two diitiuct mountain-systems traverse the United States: (1) The Pacific 
Highlands on the west, which form a part of the Cordillera of the Socky Moun- 
tains ; (2) The Atlantic Highlands, or the Appalachian system on the east. 

The Pacific Highlands includes the Eocky Mountains on the east and the 
Pacific Mountain chain ; i. e., the Cascade Mountains in Oregon and Washington 
and the Sierra Kevada Mountains in California. 

Some of the highest peaks of the Eocky Mountains are Long's Peak, Pike's 
Peak, Blanca Peak, Spanish Peak, and Fremont's Peak. 

Some of the highest peaks of the Pacific Mountain chain are Mt. Eainier, Mt 
Shasta, Mt. Whitney, and Mt. Brewer. 

The culminating point of the North American Continent is Mt. McKinley, 
in Alaska. 

The Atlantic Highlands, or the Appalachian System, include the White 
Mountains, Green Mountains, the Adirondacks, the Catskill Mountains, the 
Alleghanies, the Blue Eidge, and the Cumberland Mountains. 

There are two great low plains in the United States, the Atlantic Coast Plain, 
and the Central Plain, or the Plain of the Mississippi Valley. 

The principal rivers draining into the Atlantic are the Penobscot, Merrimac, 
Connecticut, Hudson, Delaware, Susquehanna, Potomac, Eoanoke, Cape Fear 
Santee, Savannah, Altamaha, and St. John's. 

The principal rivers draining into the Mexican Gulf are the Chattahooche 
the Alabama, the Mississippi, the Sabine, the Trinity, the Brazos, the Colorado, 
and the Eio Grande. 

The principal Pacific rivers are the Columbia, the Sacramento, the San 
Joaquin, and the Colorado. 

The Great Lakes, Superior, Michigan, Huron, Erie, and Ontario, form the 
largest system of fresh-water lakes in the world. 

The rivers and lakes of the Great Basin have no outlet to the ocean, and 
therefore form true steppe systems. 

Soda Valley in southern California and Death Valley in south-eastern Califor- 
nia are below the mean level of the sea. 

The United States extend between the isotherms of 40° and 77° Fahr., and 
therefore lie in the north temperate and in the torrid physical zones. 

A marked contrast exists between the temperature of the eastern and the 
western coasts of the northern half of the country. The eastern coasts are far 
colder than the western. 

The greater warmth of the western coasts is to be attributed to the influence 
of warm ocean currents, westerly winds, and heavy rainfalls. 

From observations dating back as far as 1738 the climate of the United States 
since that time does not appear to have undergone any decided change. 

The United States, exclusive of Alaska and its insular possessions, lies in the 
zone of the variable winds. Westerly winds, therefore, predominate. 



SYLLABUS. 367 

The rainfall is heaviest on the coasts, especially on the southern and western. 
On the Pacific coast the rainfall is heaviest in the north. On the Atlantic coast 
it is heaviest on its south. 

East of the Mississippi it may rain at any time of the year, the rainfall being 
dependent on the prevalence of the extra-tropical cyclone. West of the Missis- 
sippi the rainfall is irregular ; in parts of the Pacific Coast the rain is most 
frequent in winter. 

On the Pacific seaboard in Washington and Oregon the annual rainfall is 75 
inches. On the borders of the Gulf States it is 65 inches. On the Atlantic coast 
it varies from 40 to 50 inches. Between the eastern slopes of the Pacific range 
and the Rocky Mountains the rainfall is so scanty that agriculture is impossible 
without irrigation. 

The Weather Bureau was established for the observation of the meteorological 
conditions of the country. 

Nearly all the great storms of the United States are extra-tropical cyclones 
that cross the country in a generally easterly direction. When once started, it 
is comparatively easy to predict coming changes in the weather. 

Weather and storm signals consist of fiags designed to indicate the probable 
weather and temperature of the coming day and information concerning a 
coming storm. 

There are four characteristic plant regions in the United States: the Forest, 
the Prairie, the Steppe, and the Pacific. 

The Prairie Region lies west of the Mississippi Valley to the Plateau of the 
Great Plains. It is covered with grasses and flowering herbs. 

The Steppe Region lies between the western limits of the Great Plains to 
the Sierra Nevada and Cascade Ranges. It has a scanty vegetation, mainly the 
cactus and wild sage, and in some places is practically a desert. 

The Pacific Region lies between the western limits of the Steppe Region and 
the Pacific Ocean. In Washington and Oregon and on the mountain slopes gen- 
erally, dense forests occu.r. 

The Forest Region lies mainly east of the Mississippi ; the characteristic trees 
are the pine, spruce, hemlock, fir, juniper, beech, maple, birch, alder, oak, and 
poplar. 

The principal large animals of the United States are those which have been 
domesticated, as the horse, ox, cow, sheep, mule, goat, and dog. 

Among wild animals are the black bear, panther, deer, grizzly bear, wolf, and 
manatee, or sea-cow. 

The principal agricultural productions are wheat, corn, rye, oats, barley, buck- 
wheat, hay, hops, flax, tobacco, rice, cotton, and sugar. 

Named in the order of their money values the principal mineral products of 
the United States are pig iron, bituminous and soft coal, copper, anthracite or 
hard coal, gold, silver, petroleum, building stone, natural gas, and lead. 

The principal metals named in the order of their money values are iron, 
copper, gold, silver, lead, zinc, aluminium, and mercury. 



368 PHYSICAL GEOGRAPHY. 

The Territory of Alaska has an area of 580,107 square miles, and is nearly 
one-fifth that of the area of the rest of the continental domain of the United 
States. 

Bering Sea on the west, and the Gulf of Alaska on the south, are the prin- 
cipal indentations of the coast. Bristol Bay, Kuskokwim Bay, Norton Sound, and 
Kotzebue Sound are among the most important of the smaller indentations. 

The principal islands are St. Lawrence Island, Nunivak, and the Pribyloff 
Islands in Bering Sea, the Aleutian Islands, Kodiak Islands, and the Alex- 
ander Archipelago, including Baranofi", Chichagof, Kupreanof, and Prince of 
Wales Islands. 

The northern portions of Alaska are low and flat, and are covered by tundras 
or frozen moor-lands. The rest of the country is generally mountainous, and is 
traversed by prolongations of the Pacific Mountain system of North America. 
Mts. McKinley and St. Elias are the principal peaks. 

The principal river of Alaska is the Yukon, which is some 2000 miles long, 
and is one of the largest rivers of the North American Continent. The Kusko- 
kwim is the only other important river. The Yukon has a delta mouth — the 
Kuskokwim, an estuary. 

The climate of Alaska is cold and wet, though under the combined influences 
of the Japan Current, the rains, and the warm south-westerly winds, the climate 
is less severe than at corresponding latitudes in the interior or on the Atlantic 
coast. 

Dense growths of grasses abound during the brief summer. Forests of cedar 
and spruce cover portions of the lower mountain slopes and river valleys. 

The chief animals are the polar and brown bears, the mink, black or silver 
fox, the moose, and the caribou. The whale is found in the waters off the north- 
ern shores; the seal and the sea-otter are sources of wealth by reason of their 
valuable furs. The walrus is killed by the natives for its flesh, oil. and tusks. 
Salmon, halibut, cod, and herring are the principal food fish. 

Deposits of coal, silver, gold, copper, iron, and lead occur in difierent parts 
of the country. 

The inhabitants consist of various elements, the principal of which are the 
Esquimaux, the Indians, the Aleuts, the Creoles, and the people of the archi- 
pelagoes of the southern and south-eastern coast, together with a constantly 
increasing white population attracted by the extensive gold deposits. 

Sitka, on Baranoif Island, is the principal settlement. 

The recently acquired insular possessions of the United States are the Philip- 
pine Islands, the Hawaiian or Sandwich Islands, Porto Eico, Guam, in the Mari- 
anne group, Tutuila, in the Samoan group, and Wake Island. 

The Philippine Islands are south-east of China and east of Anam. Luzon, 
Mindanao, Samar, Panay, Palawan, Mindoro, Leyte, Negros, Cebu, Masbate, and 
Bohol are the principal islands. The area of all the islands is about 140.000 
square miles. 

The principal agricultural products are rice, com, hemp, sugar, tobacco, cocoa- 



SYLLABUS. 369 

nuts, and cacao. Undeyeloped deposits of coal or lignite, petroleum, copper, iron, 
and lead are said to exist. 

Dense forests which furnish valuable hard woods cover large areas in all the 
islands. The bamboo is common. 

The Philippines lie in the tropics. The climate is therefore hot, especially in 
the southern portion. The south-west monsoon brings heavy rains from May to 
October. The annual rainfall in some parts of the islands is 114 inches. 

Severe typhoons occur in Luzon. Severe earthquakes and active volcanoes 
characterize the Philippines. 

The Hawaiian or Sandwich Islands are situated near the middle of the North 
Pacific, south of the Tropic of Cancer. They possess, therefore, a tropical 
climate. 

Hawaii, Maui, Oahu, Kauai, Molokai, and Lanai are the principal islands. 
The area of all the islands is about 6740 square miles. Honolulu, on Oahu, is 
the principal city. 

The Hawaiian Islands are of volcanic origin. On the coasts the climate is 
tropical. On mountain slopes that face the prevailing winds the annual rainfall 
in places reaches 179 inches. 

The principal agricultural products are sugar and coffee. Tropical fruits, 
such as bananas, pineapples, oranges, lemons, etc., are plentiful. Extensive 
forests exist. 

Porto Eico is the most eastern and the smallest of the Greater Antilles. It is 
situated 60 miles east of Hayti. Its area is approximately 3670 miles. It has a 
heavy rainfall and a fertile soil. Its principal agricultural products are sugar, 
coffee, tobacco, cotton, maize, and rice, together with various tropical fruits. It 
possesses valuable forests and valuable mineral deposits. 

Guam, the principal of the Ladrone or Marianne Islands, is situated in the 
Pacific Ocean north-east of the Philippines, about 900 miles from Manila aud 
5200 miles from San Francisco. 

Tutuila, one of the Samoan Islands, is situated in the tropical southern Pacific, 
4000 miles from San Francisco, 2200 miles from Hawaii, and 4200 miles from 
Manila. It contains the magnificent harbor of Pago-Pago. 

Wake Island is a lonely island in the mid-Pacific, some 1300 miles east of 
Guam and 2000 miles west of Honolulu. 

REVIEW QUESTIONS- 

State the geographical position of the United States, excluding its insular 
possessions and Alaska. 

Describe the peculiarities of its coast lines. 

Name the principal indentations of the eastern coast. Of the western coast. 

In what respect do the islands which lie north of Cape Cod differ from those 
which lie south of it? 
24 



370 PHYSICAL GEOGRAPHY. 

What is the origin of the islands oflf the southern coast of Florida ? 

Describe the Pacific Highlands. Of what mountains do these consist ? Locate 
the Great Plains. The Great Basin. 

Name the principal peaks of the Eocky Mountains. Of the Pacific Mountain 
chain. 

Describe the Atlantic Highlands or the Appalachian System. 

Name the great low plains of the United States. 

Describe the lake-systems of the United States. 

What system of inland drainage is found in the United States ? 

In what mathematical zone is the United States situated ? In what physical 
zones ? 

Between what isothermal lines does the United States extend ? 

What difference exists between the climate of the eastern and western coasts ? 
What are the causes of this diiference ? 

In what wind zone does the United States lie? 

In what parts of the country does the heaviest annual rainfall occur ? The 
smallest annual rainfall ? 

For what was the Weather Bureau established ? Describe the following storm 
or weather signals employed by the U. S. Weather Bureau ; viz., the temperature 
signal ; the clear or fair weather signal ; the rain or snow signal ; the cold wave 
signal ; the storm signal ; the information signal. How would the signal flags 
be displayed to indicate an approaching storm, followed by a cold wave? 

Under what four characteristic plant regions may the vegetation of the United 
States be arranged ? 

Describe the location of each of these regions. 

Name the principal forest trees of the United States. 

Name the principal domesticated and wild animals of the United States. 

Enumerate the principal agricultural productions. 

Name the principal corn-producing States. The principal wheat-producing 
States. 

Name the principal cotton-producing States. The principal rice-producing 
States. The principal sugar-producing States. 

Name, in the order of their money value, the principal mineral products of 
the United States. Name in the same order the most important metals. 

Where are the principal coal-fields of the United States situated ? The princi- 
pal coal-oil or petroleum fields? The principal fields of natural gas? The 
principal beds of salt? 

What are the limits of the Territory of Alaska ? State its boundaries. What 
is its area ? 

Name the principal indentations of the coast of Alaska. What is the extent 
of its coast line ? . 

Name the principal islands of the western coast. Of the southern coast. 

Describe the surface structure of Alaska. 

Describe the river-system of the Yukon. Where is the Kuskokwim River ? 



SYLLABUS. 371 

What is the general climate of Alaska ? 

Describe the vegetation of Alaslia. What are the principal trees? 

Name the principal food lish of Alaska. Name the principal fur-bearing 
animals. What other large animals are found in the country? 

Name some of the different people who inhabit Alaska. Name the principal 
settlement of Alaska. 

Name the most important of the insular possessions of the United States. 

Name the principal islands of the Philippines. 

What is the number and the combined area of the Philippine Islands ? 

Name and locate the principal city. 

Name the principal agricultural products of the Philippines. What mineral 
deposits are said to exist ? What kinds of forests exist ? 

Describe the climate of the Philippines. When does the rainy season occur? 

Name the principal of the Hawaiian or Sandwich Islands. The principal city. 
Describe the surface structure of the Hawaiian Islands. Describe the climate. 
Name the principal agricultural productions. 

What is its approximate area of Porto Eico ? Name its principal agricultural 
productions. Describe its climate. 

Where is Guam Island ? Tutuila Island ? Wake Island ? State some import- 
ant fact concerning each. 

MAP QUESTIONS* 

Describe from the Physical Map of the United States the surface structure of 
the country, giving the relative position of the High Lands and Low Lands. 

Describe the Pacific Highlands. 

Describe the Atlantic Highlands or the Appalachian System. 

Locate the Black Hills ; the Wahsatch Mountains ; the Sierra Nevada ; the 
Cascade Mountains ; the Coast Mountains ; San Luis Park; Pike's Peak ; Long's 
Peak ; Fremont's Peak ; Mt. Eainier ; Mt. Shasta ; Mt. Whitney ; Mt. McKinley. 

Describe the drainage of the Great Lakes. 

Name the principal rivers which empty into the Atlantic. Into the Gulf of 
Mexico. Into the Pacific. Name the principal tributaries of the Mississippi. 

Where are the Santa Barbara Islands? The Bahama Islands? Vancouver's 
Island? 

What is the cause of the southward deflection of the isothermal lines in the 
western part of the United States ? 

In what portions of the United States is the lowest mean annual temperature 
found? The highest? 

Locate the principal indentations of the coast of Alaska. Locate its principal 
islands. Its principal river systems. Locate the two highest mountain peaks. 

Where are the Philippine Islands situated? Locate Luzon, Mindanao, Samar 
Panay, Palawan, Mindoro, and Negros. 

Locate the Hawaiian or Sandwich Islands. Locate Porto Eico, 



372 PHYSICAL OEOOBAPHY. 

GENERAL SYLLABUS. 

Physical Geography treats of the distribution of the land, water, air, plants, 
animals, and minerals of the earth. 

The rotundity of the earth is proved : (1) By the appearance of approaching 
or receding objects; (2) By the circular shape of the horizon; (3) By the shape 
of the earth's shadow ; (4) By actual measurement. 

Exact geographical position is determined by reference to certain imaginary 
circles called parallels and meridians. 

Maps are drawn on different projections : the Equatorial, the Polai-, Merca tor's, 
and Grail's, a variety of Merca tor's projection, are in the most general use. 

The rotation of the earth is proved : (1) By Foucault's pendulum ; (2) By the 
deviation in the direction of falling bodies, winds, and ocean currents. It is 
rendered probable by analogy. 

The change of seasons is caused by the revolution of the earth, together with 
the inclination of the earth's axis at an angle of 66° 33' to the plane of its orbit, 
and the constant parallelism of the axis with any former position. 

The proofs of the present highly heated condition of the interior of the earth 
are as follows : 

(1) The deeper we penetrate the crust, the higher the existing temperature. 

(2) The presence of volcanoes, which, in all latitudes, eject melted rock from 
the inside of the earth. 

(3) Careful geological observations which prove that the earth's surface is 
never at rest, but is gradually sinking in some places and rising in others. 

The gradual cooling of the heated and potentially plastic interior causes : (1) 
Crater or volcanic eruptions ; (2) Fissure or sheet eruptions ; (3) Gradual changes 
of level ; (4) Earthquakes. 

Volcanoes eject from the interior of the earth: (1) Melted rock or lava; (2) 
Ashes or cinders ; (3) Vapors or gases. 

Nearly all volcanoes are found near the coasts of the continents or on islands. 

The principal volcanic regions of the earth are : (1) Along the shores of the 
Pacific; (2) In the islands of the Pacific; (3) In the neighborhood of the seas 
that divide the northern and the southern continents; i. e., the Caribbean Sea, 
the Mediterranean and Red Seas, and in the Pacific and Indian Oceans between 
South-eastern Asia and Australia ; (4) In the northern and central parts of the 
Atlantic Ocean; (5) In the western and central parts of the Indian Ocean. 

Fissure or sheet eruptions occur : (1) As extensive vertical sheets filling great 
fissures in the rocks of all geological formations; (2) As extensive horizontal 
sheets between parallel strata, or spread out over vast areas of the bed of an 
ocean or the earth's surface; (3) In dome-shaped masses called laccoliths or 
laccolites. 

Earthquake shocks are more frequent: (1) In winter than in summer; (2) At 
night than during the day ; (3) During the new and full moon than during any 
other phase. 



OENEBAL SYLLABUS. 373 

Bocks maybe divided, according to their origin, into four classes: (1) Igne- 
ous; (2) Aqueous; (3) Metamorphic; (4) iEolian. 

Rocks may be divided according to their condition into: (1) Stratified; (2) 
Unstratified. 

Unstratified rocks are either igneous or metamorphic. 

Aqueous rocks are sometimes called sedimentary. 

During the geological past extensive changes occurred in the land and water 
surface of the earth, and in the plants and animals inhabiting it. 

There were six geological eras : (1) The Azoic era ; (2) The Eozoic era ; (3) The 
Palseozoic era ; (4) The Mesozoic era ; (5) The Cenozoic era ; (6) The Era of Man. 

The agencies now causing changes in the earth are : (1) Erosion or denuda- 
tion ; (2) Wind corrasion and transportation ; (3) Avalanches and land-slides ; 
(4) Ocean waves; (5) Man. 

Erosion is due to three agencies : (1) Weathering ; (2) Corrasion ; (3) Trans- 
portation. 

The principal agencies that cause weathering are : (1) Heat and cold ; (2) 
Alternate freezing and thawing ; (3) Eusting, corrosion, and solution. 

Of the 197,000,000 square miles of the earth's surface, 144,000,000 square miles 
are covered by water, and 53,000,000 by land. The proportion between the land 
and water is very nearly as the square of three is to the square of five. 

Nearly all the land masses are collected in one hemisphere, and a large part 
of the water in another. 

There are two great systems of trends or lines of direction, along which the 
shores of the continents, the mountain-ranges, the oceanic basins, and the island 
chains extend. 

The coast lines of the northern continents are very irregular, the shores being 
deeply indented with gulfs and bays, while those of the southern continents are 
comparatively simple. 

Of the 53,000,000 square miles of the land, 3,000,000, or about one-seventeenth, 
is composed of islands. 

Islands are either continental or oceanic. Continental islands are detached 
portions of the neighboring continents. Oceanic islands are either high or low, 
the high oceanic islands are generally of volcanic formation ; the low islands are 
of coral formation. 

There are four varieties of coral formations : (1) Fringing reefs ; (2) Barrier 
reefs ; (3) Encircling reefs ; (4) Atolls. 

The earth's surface is composed of high lands and low lands. The dividing 
line is 1000 feet above the level of the sea. High lands are either mountains 
or plateaus. Low lands are either hills or plains. 

According to their origin plains are: (1) Undulating; (2) Marine; (3) Allu- 
vial. According to their position they are : (1) Coastal ; (2) Inland ; (3) Worn- 
down mountain low-la-nds, old plains, or peneplains. According to the materials 
that form them they are : (1) Eiver-made ; (2) Dust ; (3) Lava. 



374 PHYSICAL GEOOBAPHY. 

According to their position plateaus are: (1) Marginal; (2) Intermont. 
According to their age they are : (1) Young or immature ; (2) Old or matured. 

As the earth cooled its interior shrank away from the crust. Enormous lat- 
eral pressures were produced in the crust as it slowly accommodated itself to the 
new conditions. These pressures fractured the crust, folded or bent it, or caused 
it slowly to rise in some places and to sink in others. 

Mountains were formed: (1) By flexure; (2) By fracture; (3) By the injection 
of lava between strata. 

The following peculiarities are noticeable in the relief forms of the conti- 
nents : 

(1) The continents have, in general, high borders and a low interior. 

(2) The highest border lies nearest the deepest ocean. 

(3) The greatest prolongation of a continent is always that of its predominant 
mountain-system. 

(4) The prevailing trends of the mountain masses are the same as those of 
the coast lines, and are, iu general, either north-east or north-west. 

Water acquires its maximum density at about the temperature of 39.2° Fahr. 

Water requires more heat to warm it, and gives out more on cooling than any 
other common substance. 

The drainage of the land is of two kinds : (1) Subterranean ; (2) Surface. 

Surface drainage is either oceanic or inland. 

Springs are : (1) Hill-side ; (2) Fissure ; (3) Artesian. 

Constant springs have large reservoirs; temporary springs, small reservoirs. 
Hot springe either have deep-seated reservoirs, or their reservoirs are near beds of 
recently ejected lava. The principal mineral springs are silicious, sulphurous, 
chalybeate, brines, and acidulous. 

The quantity of water discharged by a river depends : (1) On the size of its 
basin ; (2) On the amount of its rainfall. 

The material eroded by a river is deposited : (1) In the channel of the river ; 
(2) On the alluvial flats or flood-grounds ; (3) At the mouth ; (4) Along the coast 
near the mouth. 

In the upper courses of rivers erosion occurs mainly on the bottom of the 
channel ; in the lower courses, at the sides. 

The gradual elevation of river basins may engraft or unite several indepen- 
dent rivers in a single river system. Its gradual depression dismembers the 
tributaries of a system, or causes them to become separate rivers. 

In the Northern -Hemisphere the earth's rotation causes a river to tend to 
corrode its right bank more than its left bank, and in the Southern Hemisphere, 
its left bank more than its right bank. 

The Atlantic and Arctic Oceans receive the waters of nearly all the large river 
systems of the world. 

Lakes are : (1) Lakes of new land-areas ; (2) Delta lakes ; (3) Lagoon or sea- 
shore lakes ; (4) Glacial lakes ; (5) Playa lakes. 

Some prehistoric lakes are : (1) Agassiz ; (2) Bonneville ; (3) Lahontan. 



QENEBAL SYLLABUS. 375 

Lakes have a comparatively short life because : (I) Their basins are filled by 
sediment from their inflowing streams ; (2) Their outlets are cut down by theii 
outflowing streams. 

The bed of the ocean is less diversified than the surface of the land. 

The greatest depth of the ocean is, probably, greater than the greatest elevation 
of the land. 

The articulation of land and water assumes four distinct forms — inland seas, 
border seas, gulfs and bays, and fiords. 

Inland seas characterize the Atlantic ; border seas the Pacific ; gulfs and bays 
the Indian ; fiords the Atlantic and Pacific. 

The Pacific occupies about one-half of the entire water area of the earth, the 
Atlantic about one-quarter, the Indian about one-fifth, the Antarctic about one- 
seventeenth, and the Arctic about one thirty-fifth. 

A deposit of fine calcareous mud or ooze, formed of the hard parts of minute 
animalculee, occurs over extended areas of the floor of the ocean. 

Tides are caused by the attraction of the sun and moon : spring tides by their 
combined attractions ; neap tides by their opposite attractions. 

Constant ocean currents are occasioned by the heat of the sun and the rotation 
of the earth. 

The vertical rays of the sun are warmer than the oblique rays : (1) Because 
they are spread over a smaller area ; (2) Because they pass through a thinner 
layer of air ; (3) Because they strike the surface more directly, and, therefore, 
produce more heat. 

Continual summer characterizes the tropics; summer and winter of nearly 
equal duration, the temperate zones ; and short, hot summers, followed by long, 
intensely cold winters, the frigid zones. 

The principal modifiers of climate are : (1) The distribution of the land- and 
water-areas ; (2) The varying elevation of the land ; (3) The slope of the land ; 
(4) The position of the mountain-ranges ; (5) The nature of the surface ; (6) The 
distribution of the winds and moisture ; and (7) The ocean currents. 

Winds are caused by the disturbance of the equilibrium of the atmosphere 
by heat. 

The general motion of the surface winds is toward an area of greatest heat ; 
of the upper currents, toward an area of smaller heat. 

The general atmospheric circulation is from the equator to the poles, and from 
the poles to the equator. 

The principal wind zones are : (1) The zone of equatorial calms ; (2) The zones 
of the trades ; (3) The zones of the calms of Cancer and Capricorn ; (4) The zones 
of the prevailing westerly winds ; (5) The zones of the polar winds. 

Cyclones are : (1) Tropical cyclones ; (2) Temperate latitude or extra-tropical 
cyclones. They are both travelling areas of low barometer. The passage of an 
extra-tropical cyclone is frequently attended by warm waves in front of the 
storm and cold waves in its rear. Anti-cyclones are travelling areas of high 
barometer. 



376 PHYSICAL GEOGRAPHY. 

Moisture may be precipitated from the air in the form of dew, mist, fog, olond, 
rain, hail, sleet, or snow. 

In order that any form of precipitation may occur, the air must be reduced 
below the temperature of its dew-point. 

Glaciers are masses of ice and snow, which move with extreme slowness down 
the higher valleys of mountain-ranges. They resemble rivers in that they 
receive, through the drainage of their basins, the solid material which flows into 
them. 

Glaciers are : (1) Alpine ; (2) Piedmont; (3) Continental. Moraines are lateral, 
medial, terminal, frontal, and ground. Till, and other glacial deposits, assume 
shapes called drumlins, eskers, kames, and valley trains. 

The snow line is the distance above the level of the sea where the snow 
remains throughout the year. The height of its lower level above the sea 
depends: (1) On the amount of the snowfall; (2) On the temperature of the 
valley; (3) On the inclination of the slope. 

The unit of electric potential is called a volt; the unit of electric current, aij 
ampere ; the unit of electric resistance, an ohm. 

The principal electric phenomena of the atmosphere are thunder and light- 
ning, St. Elmo's fire, and the Auroras. 

The principal optical phenomena are the rainbow, the mirage, halos, and 
eoronse. 

The earth acts like a huge magnet. Its magnetism is, probably, due to the 
circulation around it of electrical currents generated by the sun's heat. 

The true basis for the distribution of vegetation is the distribution of light, 
heat, and moisture, upon which its existence mainly depends. 

The variety and luxuriance of vegetation decrease as we pass from the equa- 
tor to the poles, or from the base of a mountain to the summit. 

Only those plants that contain green coloring matter can, by photosynthesis, 
prepare their own food by materials taken directly from the soil. The principal 
plant groups or societies are : (1) Water plants;. (2) Drought plants; (3) Plants 
occupying a position intermediate between water and drought plants; (4) Salt 
plants. 

Forests are : (1) Evergreen foliage ; (2) Deciduous ; (3) Coniferous ; (4) Leaf- 
less ; (5) Swamp. 

Deserts are : (1) Tropical ; (2) Cactus ; (3) Salt and alkaline. 

The principal food-plants of the tropical regions are rice, bananas, plantains, 
dates, cocoanuts, cassava, bread-fruit, sago, and yams. 

Coffee, tea, cocoa, pepper, cloves, nutmegs, and vanilla are products of the 
tropics. 

The principal food-plants of the temperate zones are barley, rye, wheat, oats, 
maize or Indian corn, buckwheat, and potatoes. 

Animals are restricted by conditions of food and climate to certain regions of 
tbe earth. They are dependent for their continued existence upon plants. 

With a few exceptions animals possess but little power of becoming accli- 



GENERAL SYLLABUS. 377 

mated or living in a climate differing greatly from that in which they were 
created. 

The principal physiographical barriers opposing the dispersal of animals are : 
(1) Large bodies of water ; (2) Extensive and elevated mountain-ranges ; (3) 
Deserts ; (4) Forests. The principal physiological barriers are : (1) Food condi- 
tions; (2) Climate. 

The principal animal realms or regions are: (1) The Nearctic; (2) The Neo- 
tropic; (3) The Palsearctic ; (4) The Ethiopian; (5) The Oriental; (6) The Aus- 
tralian. 

Marine fauna are : (1) Littoral; (2) Pelagic ; (3) Abyssal. 

The entire human family has descended from a single pair or species. 

The primary races of men are the Caucasian, the Mongolian, and the Negro. 
The secondary races are the Malay, the American, and the Australian. 

Mineral veins are : (1) Veins of segregation ; (2) Veins of infiltration ; (3) 
Fissure veins. 

The United States, exclusive of its insular possessions and Alaska, has an area 
of 3,026,500 square miles. 

The coast line of the United States is comparatively simple and unbroken. 

The predominant mountains are in the west ; the secondary mountains are in 
the east. 

The great low plains of the United States are the Atlantic Coast Plain and the 
Central Plain, or the Plain of the Mississippi Valley. 

The United States lies in the physical north temperate and the physical torrid 
zones. 

The United States, exclusive of Alaska and its insular possessions, lies in the 
zone of the prevailing westerly winds. The heaviest rainfall is on the coasts, 
especially on the west and south. There are four distinct plant regions: the 
Forest, the Prairie, the Steppe, and the Pacific. 

The Territory of Alaska occupies an area of about 580,000 square miles. It is 
mainly mountainous. The shore lands of the Arctic are frozen moorlands like 
the tundras of Asia. The Yukon and Kuskokwim are the principal rivers. 
Myriads of salmon visit the rivers during the breeding season. Valuable food- 
fish are found in the waters off the coasts. Numerous fur-bearing animals are 
found. 

Named in the order of their money value, the principal mineral products of 
the United States are pig iron, bituminous coal, copper, anthracite coal, gold, 
silver, petroleum, building stone, natural gas, lead, cement, zinc, brick clay, salt, 
and mineral waters. 



378 PHYSICAL GEOQBAPHY. 

GENERAL REVIEW QUESTIONS. 

Mathematical Geography. 

Name the planets in their regular order from the sun. 
What is the position of the solar system in space ? 
State briefly Laplace's nebular hypothesis. 
Of what use are latitude and longitude in geography ? 
Distinguish between Mercator's, eqaatorial, polar, and conical projections. 
Upon what does the difference in the length of the day and night at difierent 
seasons of the year depend ? 

Explain the causes of the change of seasons. 

The Land. 

Enumerate the proofs of the present heated condition of the interior of the 
earth. 

What do you understand by the phrase, " A potentially plastic interior" ? 

Distinguish between fissure and crater eruptions. Define laccoliths; dike; 
caldera. 

Distinguish between primary and secondary volcanic eruptions. 

Name five principal regions of active volcanoes. 

What facts have been discovered respecting earthquake shocks ? 

Name some parts of the earth that are slowly sinking. Name some parts that 
are slowly rising. 

Explain the origin of coal. 

Enumerate some of the changes which are now taking place in the crust of 
the earth. 

Define rock ; mineral ; loam ; marl. 

Into what four classes may rocks be divided according to their origin ? 

Name the six geological eras. 

Define rock weathering. Name some of the more important agencies that 
cause weathering. 

Define erosion ; corrasion ; transportation ; denudation ; deposition. 

What are the relative land- and water-areas of the earth? 

Describe the land hemisphere. The water hemisphere. 

What do you understand by lines of trend ? 

Which of the continents contains, in proportion to its area, the greatest length 
©f coast line ? Which the least ? 

Distinguish between continental and oceanic islands ; between coral and vol- 
canic islands. 

State Darwin's hypothesis for the formation of coral islands. Give some other 
hypotheses for coral formations. 

Define each of the following varieties of plains : alluvial, fluviatile, marine, 
coastal, inland, peneplain, dust, lava. 



GENERAL SYLLABUS. 379 

Distinguisli between marginal and intennont plateaus. 

How can the cooling of the earth's interior cause mountains? 

What peculiarities are noticeable in the general relief forms of the conti- 
nents? 

Which of the continents resemble each other in the general arrangement of 
their relief forms ? In what respect do they all resemble one another ? 

The Water. 

Enumerate some of the properties of water that enable it to play such an 
important part in the economy of the earth. 

Distinguish between subterranean and surface drainage. 

Distinguish between hill-side, fissure, and artesian springs. Between constant 
and temporary springs. Name some of the principal mineral springs. 

Define river-system, basin, water-shed, source, channel, and river-mouth 

Explain the origin of waterfalls. 

By what are the inundations of rivers caused ? 

What is silt ? In what different parts of a river-system may silt he deposited ? 
Define fluvio-marine formations. 

What do you understand by a dismembered river? By an engrafted river? 
By a drowned river? 

Classify lakes. Name some of the principal ways in which lake basins may 
be formed. 

Why are lakes necessarily temporary drainage features? 

In what two ways may salt lakes be formed ? 

Name the great fresh-water lake systems of the world. , 

State the composition of ocean water. What is its density ? Its boiling point ? 
Its color? 

How do the five oceans compare with one another in area? 

Distinguish between inland seas, border seas, gulfs and bays, and fiords. 

Explain the origin of the ooze deposits on the ocean's beds. 

Define cauldron ; furrow ; trough ; bank ; shelf. 

In what parts of the Pacific, Atlantic, and Indian Oceans are most of the deep 
depressions situated ? 

By what are waves caused ? Upon what does their height depend ? 

How are tides caused? Distinguish between ebb, fiood, spring, and neap 
tides. 

Where does the parent tidal wave originate ? 

In what part of the (jcean are tides the highest? Why? 

What are the main causes of constant oceanic currents ? 

In what respects do the currents in the three central oceans resemble one 
another ? 

The Atmosphere. 

Name six constituents of the atmosphere. 

Explain the operation of the thermograph. Of the barograph. 



380 PHYSICAL GEOGRAPHY. 

By what instrument is tlie pressure of the atmosphere measured ? 

What proof have we that the greater weight of the atmosphere lies within a 
few miles of the earth's surface ? 

Define climate. Name the principal modifiers of climate. 

Why are the vertical rays of the sun warmer than the oblique rays ? 

In what diiferent ways does the atmosphere receive its heat from the sun ? 

Explain the origin of winds. 

Define barometric gradient ; isobaric chart. 

Name the principal regions of tropical cyclones. 

Distinguish between tropical and extra-tropical cyclones. 

What influence, on the precipitation of moisture, is believed to be exerted by 
the dust particles in the atmosphere ? 

Name the different wind zones of the earth. 

What is the origin of land and sea breezes ? What resemblance do land and 
sea breezes bear to monsoons ? 

What facts have been discovered in regard to the extended storms of the 
United States? 

Enumerate the circumstances upon which the rapidity of evaporation depends. 

State the general law for the occurrence of precipitations. 

Name the primary forms of clouds. The secondary forms. 

Explain the peculiarities of the rainfall in each of the wind zones. 

Define snow line. On what three circumstances does the height of the snow 
fine depend? 

Describe the formation of a glacier. Name three types of glaciers. 

Name some of the evidences of the existence of a former glacial epoch in North 
America. 

Enumerate the principal electrical and optical phenomena of the atmosphere. 

What is the probable cause of the earth's magnetism ? 

Define volt, ohm, ampere. What analogies exist between the flow of water 
in a pipe and an electric current ? 

Plant Life and Animal Life. 

Why should the distribution of light, heat, and moisture form the best basis 
for the distribution of vegetation ? 

Define photosynthesis ; proteids ; protoplasm. 

Define flora. Distinguish between the horizontal and the vertical distribution 
of vegetation. 

State the names and limits of the horizontal zones of vegetation. What are 
the characteristic features of the flora of each of these zones ? 

State the conditions requisite for the existence of forests ; of prairies ; of 
steppes; of deserts. 

Into what difierent classes may forests be divided ? Deserts? 

Enumerate the principal cultivated plants of the torrid, temperate, and polar 
ksoes. 



GENERAL SYLLABUS. 381 

Define fauna. Upon what is the existence of animal life dependent? 

Name the principal animal regions or realms. State briefly the limits of each 
realm. Name a few characteristic animals in each realm. 

Enumerate the proofs of the probable unity of the human race. 

Name the portions of the world inhabited by each of the primary and second- 
ary races. 

Minerals. 

Name the principal useful metals. Enumerate the most important natural fuels. 
In what parts of the world are valuable deposits of coal found ? 
Name some of the important gold-fields of the earth. 

Physical Features of tlie United States. 

What is the area of the United States exclusive of Alaska and the recently 
acquired insular possessions? 

Describe the surface structure of the United States and its drainage-systems. 

What are the causes of the difierence in the temperature of the eastern and 
western coasts? 

In what wind zone is the United States situated ? Describe briefly the charao 
teristics of the mean annual rainfall. Name the four principal regions of vege- 
tation. Enumerate the chief agricultural productions of the country. 

What large animals are found in the United States ? 

Name the chief mineral productions of the United States. 

What is the area of Alaska? What are the principal indentations of its 
coast? Name its principal islands. Describe the river-system of the Yukon. 

Name the insular possessions of the United States. 

GENERAL MAP QUESTIONS. 

Volcanoes and Eartliquakes. 
Describe the volcanic districts of the Pacific Ocean. In what portions of these 
districts are volcanoes most numerous ? 

Describe the volcanic districts of the Indian Ocean. 

Describe the volcanic districts of the Atlantic. 

What portions of the world are especially liable to earthquake shocks? 

Geological Formations of the Earth. 

Trace on the map the principal regions of the earth where rocks formed by 
volcanic and younger eruptive flows occupy the surface. Trace in a similar 
manner the regions where the archseic rocks and granites occupy the surface. 
Where the Palaeozoic rocks occupy the surface. The Mesozoic. The Tertiary 
and Desert sandstones. The Quaternary. 

What portions of the earth's surface are occupied by sandy and desert wastes ? 
Over what portions are the exact character of the geological formations unknown? 



382 PHYSICAL GEOGRAPHY. 

Oceanic Basins, Areas, and Eiver-systems. 

What two oceans receive the drainage of the greatest areas of the continents^ 

State, from a careful inspection of the direction in which the principal river- 
systems flow, the direction of inclination of the principal slopes of each of the 
continents. 

Locate the principal systems of inland drainage in each of the continents. 
Name the principal lakes and rivers belonging to each of these systems. 

Name the principal rivers draining into the Atlantic. Into the Pacific. Into 
the Indian. Into the Arctic. Name the principal rivers of the world which have 
delta mouths. 

Name the land and water boundaries of each of the five oceans. 

Describe briefly some peculiarities of the bed of the Atlantic Ocean. Of the 
Pacific Ocean. Of the Indian Ocean. 

Ocean Ciirrents. 

What is the general direction of the equatorial ocean currents ? Explain the 
eause of this general direction. What exception can you find to it ? 

What is the general direction of the Arctic currents? Of the Antarctic cur- 
rents? What are the causes of these general directions? 

Describe the principal currents of the Atlantic ; of the Pacific ; of the Indian 
Ocean. 

Name the principal warm ocean currents ; the principal cold, ocean currents. 

Name some cold currents which powerfully afiect the climate of parts of the 
earth. Name some warm currents which powerfully affect the climate. 

In what respects do the general directions of the currents in each of the cen- 
tral oceans resemble one another ? 

Name some points of resemblance between the Gulf Stream and the Japan 
Current. 

Isothermal Lines and Physical Zones. 

Point out some of the most striking deviations in the directions of the iso- 
thermal lines from the parallels of latitude. 

Explain in each case the main cause of these deviations. 

In what part of the world do the isothermal lines coincide most nearly with 
the parallels of latitude ? 

Trace on the map the isothermal line of 70° Fahr. Of 30° Fahr. 

What is the mean temperature of London for January? For July? What 
other large cities have nearly the same mean July or January temperature as 
London? 

What is the mean temperature of Bombay for January ? For July ? What 
other large cities have nearly the same mean July or January temperature aa 
Bombay ? 

Point out the northern limit of drift ice. The southern limit. 



GENERAL SYLLABUS. 383 

Describe the boundaries of the physical torrid, temperate, ana frigid zones. 
Name the principal countries which lie wholly or in part in each of these zone& 

Winds and Ocean Routes. 

State the boundaries of each of the wind zones. 

What is the general direction of the wind in each of these zones? 

Name the principal monsoon regions of the world. 

What is the direction of the rotation of the wind in the cyclonic storms of the 
northern hemisphere ? Of the southern hemisphere ? 

Name the principal tropical cyclone regions of the world. 

What would be the general route of a vessel in sailing from America to Europe, 
and back again ? From Europe to San Francisco ? 

What two sailing routes are there from Europe to Australia or India ? 

Give the northern and southern limits of drift ice. 

Vegetation. 

State the boundaries of each of the plant zones. Name the countries or por= 
tions of countries which lie in each of these zones. 

Name some of the useful plants of each of the plant zones. 

Point out on the map the northern limit of trees. The southern limit. 

Name some parts of the world where the following are cultivated: rice 
oranges, sugar, cocoa, cloves, pepper. 

Name the dliferent kinds of forests. 

What are the principal tea- and coffee-growing countries of the world ? 

Animal Begions. 

State the boundaries of the principal animal regions or realms. 

Name some animals that are found in the temperate regions of both the east- 
ern and the western continent. In the tropical region. 

In what parts of the world are the whale, seal, grizzly bear, musk-ox, and 
walrus found ? 

Ethnographic Chart. 

Trace on the map the northern and southern limits of permanent habitation. 

Name all the countries of the world inhabitated by the Caucasian race. 

In what parts of the world are the Caucasians mixed with other races ? 

Name the different countries of the world inhabited by the Mongolian race. 
Name some of the different peoples belonging to this race. 

What parts of the world are peopled by the Ethiopian, or Negro, race? Name 
some of the different tribes belonging to this race. 

Name the different countries of the world inhabited by the secondary races 
of men. Give the names of the principal tribes of each of the secondary races. 



384 PHYSICAL QEOQBAPHT. 

What different races of men inhabit North America? South America? 
Europe? Asia? Africa? Australia? 

Physical and Weather Maps of the United States. 

Describe from the map the forms of relief of the United States. 

Name the principal mountain-ranges belonging to the predominant and 
secondary mountain-systems. 

Describe the drainage-systems of the United States. What large lake-system 
is situated in the north-eastern part of the United States? 

Trace on the map the general directions of the principal isothermal lines, 
showing the hottest and coldest portions of the country. 

Name the principal islands which lie near the coasts of the United States. 

Name the fluvio-marine formations of the eastern coast. 

Name the principal islands that lie near the coasts of Alaska. 

Name the recently acquired insular possessions of the United States. 

Locate each group of islands. 

Name some of the principal products of some of the largest of these groups. 

Trace the progress of the areas of high and low barometer across the United 
States on the days indicated on the map. 

QUESTIONS RELATING TO THE PHYSICAL GEOG- 
RAPHY OF A STATE. 

In what physical region is this State principally situated ? 

Is the general surface of this State more or less than one thousand feet above 
the sea-level ? 

Into what body or bodies of water do the principal rivers of this State empty? 

Name the principal lakes located within, or that border, on this State, if any. 

Name the principal rivers or river systems that are partly or wholly situated 
in this State. 

What is a navigable river ? 

Name the navigable rivers of this State, if any. 

Name the navigable lakes in this State, or that border on the State, if any. 

Name the principal mountain system of this State, if any. 

Has this State any coast line ? If so, name its principal inlets, bays, harbors, 
points, or promontories. Name the islands that lie near the coast, if any. 

What is the general climate of this State ? When is rain most common ? 

Name the cereals of this State, 

Name the principal fruits of this State ? 

Name the other agricultural products of this State in addition to cereals and 
fruits. 

Are any wild animals found in this State ? 

Name the principal mineral products of this State. 



INDEX. 



Abyssal Fauna, 305 

Abyssinian Plateau, 116 

Acclimation, 292 

Acidulous Springs, 136 

Aconcagua, 104 

Active Volcanoes, 49 

Actual Barometric Gradient, 203 

Humidity, 222 
Adirondacks, 337 
Aerial Ocean, 186 

Movements of, 186 
Africa and Australia, Contrasts of, 118, 
119 

Approximate Dimensions of, 117 

Drainage Systems of, 151 

Fresh -water Lakes of, 155 

Salt Lakes of, 156 

Surface Structure of, 115 
Agassiz, Lake, 249 
Agencies Now Producing Changes in 

Crust, 72 
Agones, 258 

Agricultural Productions of Sandwich 
Islands, 363 

Products of Philippine Islands, 360, 
361 
Air, Elasticity of, 188 
Alaska, Inhabitants of, 358 

Mineral Deposits of, 358 
Albert Nyanza, 117 
Algonkian Period, 68 
Alleghanies, 337 
Alluvial Cones, 144 

Fans, 144 

Flats or Flood-grounds, 144, 145 

Plains, 93 
Alpine Glaciers, 239 

Shrubs, Mosses, Lichens, and Saxi- 
frages, Zone of, 276 
Alps, Mountain System of, 107 
Altai Mountains, 112 
Amazon, Selvas of, 106 

25 



American or Eed Race, 318 
Eace, Groups of, 318, 319 
Americas, Contrast of Surface Struct* 

^ ure of, 106, 107 
Ampere, 251 
Anchor Ice, 126 
Andes, Cordillera of the, 104 
Aneroid Barometer, 189 
Animal Barriers, 291 

Life, Distribution of, 294 

Eealms of, 296 
Eealms or Kegions, Enumeration of, 
297 
Annual Variation of Needle, 258 
Anthracite Coal, 70 
Anti-cyclones, 216 
Appalachian Mountain System, 102, 103, 

337 
Approximate Dimensions of North 
America, 103 
of South America, 106 
Arabia, Mountains of, 112 

Plateau of, 113 
Aral, Sea of, 114 
Archaean Period, 68 
Arctic Plateau, 102 
Argon, 187 

Armenia, Plateau of, 113 
Artesian Springs, 130, 131 

Wells, 131 
Articulation of Land and Water, 166 
Aryan Stock, Principal Groups of, 311, 

312 
Asia, Approximate Dimensions of, 114, 
115 
Drainage Systems of, 151 
Great Low Plain of, 114 
Minor, Plateau of, 113 
Peculiarities in its Drainage Systems, 

151 
Salt Lakes of, 156 
Surfaco Structure of. 111 
Asphaltum, 326 
Asteroids, 14-16 

385 



386 



INDEX. 



Astrouomical Climate, 193 
Atacama, Desert of, 106 
Atlantic Coast Plain, 337 

Currents in, 180 

Highlands, 337 

Ocean, Tidal Wave in, 175 
Atlas Mountains, 116 
Atmosphere, Composition of, 187 

Form of, 192 

Height of, 190 

Optical Phenomena of, 259 
Atmospheric Circulation, Origin of, 
202, 203 

Dust, 188 

Electricity, 251 

Equatorial Currents, 203 

Polar Currents, 203 

Pressure, 188 
Atolls or Coral Islands, 86, 87 
Aurora Boreal is, 254 
Australasian Island Chain, 85 
Australia, Approximate Dimensions of, 
118 

Drainage Systems of, 151 

Great Low Plain of, 118 

Salt Lakes of, 156 

Surface Structure of, 117 
Australian Alps, 118 

Eace, 317 

Eegion of Animals, 303 
Austria-Hungary, Mountains of, 108 
Auvergne Mountains, 109 
Avalanches, 76 
Azoic Era, 67 



Balkan Alps, 107 

Bananas and Plantains, 283 

Banks, 165 

Barley, 281 

Barograph, 190 

Barometer, 188 

Aneroid, 189 

Mercurial, 188 

Self-recording, 189, 190 
Barometric Gradient, 201 
Bavarian Plateau, 109 
Bay of Fundy, High Tides in, 176 
Bayous, 139 
Bays and Gulfs, 167 
Bery], 328 
Betel Plant, 286 
Big Horn Mountains, 99 
Birthplace of Tidal Wave, 173 
Bituminous Coal, 70 



Black Forest Mountains, 109 

Hills of Dakota, 99 

or Ethiopian Eace, 314 

Oak, 287 
Blizzards, 215 
Block Mountains, 98 

Dissected, 98 
Blue Color of Sky, 260 

Icebergs, 244, 245 

Mountains, 337 
Bogs, 156, 157 

Quaking, 281 
Bohemian Plateau, 109 
Bolivia, Plateau of, 105 
Bonneville, Lake, 154, 249 
Border Seas, 167 
Bore, 176 
Boulders, 248 
Boundaries of Oceans, 166 
Brazil, Plateau of, 105 

Wood, 287 
Bread Fruit, 284 
Breakers, 169 
Breezes, Land and Sea, 207 
Broken Plateaus, 95 
Brown or Malay Eace, 317 
Buckwheat, 282 
Building Stones, 327 
Bunsen's Theory of Geysers, 134 
Buttes, 95 

c. 

Cactus Deserts, 280 

Calcareous Springs, 135 

Calms of Cancer and Capricorn, Zones 

of, 205, 206 
Cameroons Mountains, 116 
Canon of the Colorado, 75, 336 
Cantabrian Mountains, 107 
Caoutchouc, 287 
Carboniferous Period, 69 
Carpathian Mountains, 107, 109 
Cascade Eange, 102 
Caspian Sea, 114 
Cassava, 283 

Cats' Tails or Mares' Tails, 226 
Catskill Mountains, 337 
Caucasian or White Eace, 309 
Caucasus Mountains, 110, 113 
Cauldrons, 165 
Cause of Cvclones,.210, 211 

of Deserts, 128,234 
Causes Producing Inundations of 

Elvers, 140 
Caverns, 74 
Celtic Group of Aryan Stock, 311 



INDEX. 



387 



Cenozoic Era, 71 
Cereals, Distribution of, 281 
Cevennes Mountains, 107-109 
Chalybeate Springs, 136 
Change of Day and Night, Cause of, 
29, 30 

of Seasons, Causes of, 32, 33 
Changes in Elver Courses, 139 
Characteristics of Fresh-water Lakes, 

157 
Charts, Isobaric, 190 
China, Plain of, 114 
Chlorophyll, 268 
Chocolate, 285 
Cinchona Trees, 287 
Cinnabar or Mercury Sulphide, 324 
Cinnamon, 286 
Circuit, Electric, 250 
Cirro-cumulus Clouds, 227 
Cirro-stratus Clouds, 227 
Cirrus Clouds, 226 
Civilization, Degree of, 308 
Classification of Winds, 204, 205 
Clay, 326 
Climate, 192 

and Products of Porto Eico, 365 

Astronomical, 193 

Continental, 199 

Modifiers of, 198 

Oceanic, 199 

of Philippine Islands, 362 

of Sandwich Islands, 363 
Climatic Belts, 197d 
Cloud-bursts, 216 
Qouds, 224, 225 

Primary Forms of, 226 

Secondary Forms of, 227 
Cloves, 286 
Coal, Formation of, 69, 70 

Important Deposits of, 325 

Oil, 325 
Coastal Plains, 93 
Cocoa, 285 
Cocoanut, 283-287 
Coffee, 285 
Coke, 325 
Cold Pole, 197b 

Temperate Zone of Vegetation, 274 

Waves, 215 

Winds, 216 
Color of Ocean Water, 162 
Colorado, Canon of, 75, 336 
Comets, 14 

Commercial GeogTaph,y, Definition of,12 
Condition of Earth's Interior, Hypoth- 
eses Concerning, 42 



Cone-bearing Trees, Zone of, 275, 276 
Conical Projection, 27 
Coniferous Forests, 278 
Constant Ocean Currents, 177 

General Features of, 179, 180 
Origin of, 177, 178 
Springs, 132 
Continent, Definition of, 78 
Continental Climate, 199 
Coast Lines, 82 
Glaciers, 240 

and Insular Areas, Eelation be- 
tween, 83 
Island Chains, American, 83, 84 

Asiatic, 84 
Islands, Peculiarity of Distribution 

of, 85 
Outlines, Changes in, 81, 82 
Eeliefs, IPeculiarities of, 98. 99 
Shelves, 83, 164 
Contour Lines, 28 
Convection, 201, 202 
Coral Formation, Other Hypotheses for, 
90, 91 
Variety of, 88 
Islands, 84 

or Atolls, 86, 87 
Darwin's Hypothesis for, 89 
Distribution of, 88 
Formation of, 87 
Cordillera, 96 

of the Andes, 104 
of the Rocky Mountains, 100 
Coronal, 260 
Corrasion, 75 
Co-tidal Lines, 175 
Cotton, 287 
Cotton-seed Oil, 287 
Counter-currents, 177 
Courses or Tracts of Eivers, 137 
Cradle of the Tides, 173 
Crater or Volcanic Eruptions, 43 
Cretaceous Period, 71 
Crevasses in Glaciers, 240 
Crust, Composition of, 63 

Thickness of, 42 
Crystal Mountains, 116 
Cultivated Plants, 281 
Cumberland Mountains, 337 
Cumulo-stratus Clouds, 228 
Cumulus or Heap Clouds, 226 
Currents, Utility of, 181, 182 
Cyclones, Cause of, 210, 211 

Extra-tropical or Temperate Lati- 
tude, 213, 214 
Peculiarities of, 210, 211 



388 



INDEX. 



Cyclones, Progressive Motion of, 209 
Regions of, 210 
Spiral Inflowing or Eotary Motion of, 

209 
Tropical, 209 
Cyclonic Rotation of Wind, Cause of, 
212 

D. 

Dates, 283 

Day and Night, Varying Length of, 36 

Day; Solar, Civil, Conventional, 30a 

Dead Sea, 114, 156 

Deccan, Plateau of, 113 

Deciduous Forests, 278 

Trees, Zones of, 274, 275 
Declination, Magnetic, 257 
Deep-sea Sounding Instruments, 166 
Delta, 83 

Formation, 145, 146 

Mouth, 140 

Rivers, 147 
Denudation, 72 
Deposition of Silt, 142 
Desert of Atacama, 106 

Belt of Eastern Continent, 235 
Deserts, Cause of, 128, 234, 235 

Characteristics of, 279 

Classification of, 280 

of Western Continent, 236 
Destruction of Forests, Influence of, on 

Inundations, 140 
Detritus or Silt, 142 
Development of River-system, 148 
Devonian Period, 68 
Dew, 223 

Circumstances Influencing Rapidity 
of Deposition of, 224 

Point, 222 
Dhawalaghiri, 112 
Diamond Fields, 327 
Diamonds, 327 
Difl"usion, 187 

Dimensions of the Earth, 21 
Dinaric Alps, 107 
Dipping Needle, 256b 
Direction of Slope, Eflect of, on Tem- 
perature of Air, 200 
Dirt-bedecked Icebergs, 246 
Dismembered Rivers, 142 
Dispersal of Native Species of Animals, 

290 
Dissected Block Mountains, 98 

Plateaus, 95 
Distributaries of Rivers, 146 



Distribution of Animal Life, 294 

of Cereals, 281 

of Human Race, 306 

of Moisture, Effect of, on Tempera 
ture of Air, 200 

of Vegetation, 271, 272 
Diurnal Variation of Needle, 251 
Dome-shaped Mountains, 99 
Double Continents, 79 
Dove's Law of Rotation of Winds, 206 
Dragon Mountains, 116 
Drainage, 128 

Continental, 149 

of Ice and Snow, 240 

Inland, 129 

Oceanic, 129 

Subterranean, 128, 129 

Surface, 128, 129 

Systems, 149 

Glacial Disturbances of, 249 
of the United States, 338 
Drift, Glacial, 242 
Drifts or Levels in Mines, 322 
Drought Plants, 270,, 271 
Drowned Rivers, 147 
Drumlins, 247 
Dunes, 81 
Dust, Atmospheric, 188 

Particles, Influence of, on Absorption 
of Heat by Air, 197 

Plains, 94 
Dykes, 319 



Eager, 176 

Earth, Magnetic Properties of, 256 

Earthquake Lake Basins, 153 

Motion, Varieties of, 56 
Velocity of, 56 

Shocks, Duration of, 56, 57 

Sounds Accompanying, 56 

Waves, 169 
Earthquakes, 55 

Distribution of, 58 

Facts Concerning, 55, 56 

Periodicity of, 58 

Principal Cause of, 57 
Earth's Magnetism, Possible Origin of, 

256, 257 
Eclipses, 18a 
Elasticity of Air, 188 
Elbruz Mountains, 113 
Electric Current, 250 
Electricity, Atmospheric, 251 
Electrification, 250 



INDEX. 



389 



Electromotive Force, 250 

Elevation, Effect of, on Temperature 

of Air, 199 
Embayed Mountains, 98 
Engrafted Eiyers, 142 
Eocene Epoch, 71 
Eozoic Era, 68 
Equator, Magnetic, 258 
Equatorial Calms, Zones of, 205 

Currents, Atmospheric, 203 

Projection, 27 

Winds, Eainy Character of, 230 
Era of Mammals, 71 

of Man, 71 
Erosion, 72 

Glacial, 242 

of Waterfalls, 138 
Erratic Blocks, 248 
Eskers, 247 
Estuary, 140 
Etesian Winds, 216 
Ethiopian or Black Race, 314 

Eegion of Animals, 301, 302 
Ethnography, 306 

Europe and Asia. Comparison of Eelief 
Forms of, 115 

Approximate Dimensions of, 110 

Drainage Systems of, 150 

Glaciers of, 242 

Great Low Plain of, 107, 110 

High, 107 

Low, 107 

Peculiarities in its Drainage Sys- 
tems, 150 

Eelief Forms of, 107 

Salt Lakes of, 156 

Surface Structure of, 107 

Systems of Fresh-water Lakes of, 155 
Evaporation, 221 

Circumstances Influencing Eapidity 
of, 221 
Evergreen Foliage Forests, 278 

Trees, Zones of, 274 
Extinct Volcanoes, 49 
Extra-tropical or Temperate Latitude 

Cyclones, 213, 214 
"Eye" of Storm, 209 
Eyre Lake, 118 



Falls of Niagara, 138 
Fauna, 290 

Marine, 304 
Ferrel's Law, 204 

Applied to Eiver Courses, 145 



Fiord Coasts, 249 
Fiords, 167, 248 

Origin of, 248, 249 
Fissure or Sheet Eruptions, Varieties 
of, 53, 54 

Springs, 130 

Veins, 320 

Peculiarities of, 321 
Fixed Stars, 14 
Flax, 287 ' 
Flaxseed, 287 
Flora, 268 
Fluviatile Islands, 145 

Lakes, 145 

Plains, 93 
Fluvio-marine Formations, 147, 148 
Fogs, 224 
Folk Lore, 308 
Food-plants of Tropical Eegions, 282, 

283 
Foraminifera, 167 
Foraminiferal Land, 167 
Forests, 276 

Classification of, 278 

of Philippine Islands, 361, 362 
Formation of Soil, 269 
Forms of Eelief of the Land, 91, 92 
Fossils, 66 

France, Mountains of, 108 
Fresh Lakes, 152 

Water Lakes, Characteristics of, 157 
Frontal Moraines, 242 
Fruits of the Tropical and Warm Tem- 
perate Zones, 285 
Furrows, 165 

G. 

Gairdner, Lake, 118 

Galena, or Lead Sulphide, 324 

Gall's Projection, 26 

Ganges and Brahmapootra, Delta of, 147 

Gangue, 320 

Garnet, 328 

Gas, Natural, 325 

Gems, 327 

General Features of Constant Ocean 

Currents, 179, 180 
Geographic Influences, Effect of, on 
Animal Eegions, 298 
on Civilization of Caucasian Eace, 

312 
on Civilization of Ethiopian Eace, 

316 
on Civilization of Yellow Eace, 
313 



390 



INDEX. 



Geographical Distribution of Glaciers, 

242, 243 
Geography, Branches of, 11 

Plant, 268 

Zoological, 290 
Geological Time, Divisions of, 67 
Germany, Mountains of, 108 
Geyser Eegions, 135 
Geysers, 133, 134 

Bunsen's Theory of, 134 
Ghauts, Eastern and Western, 113 
Glacial Deposits, 242 

Drift, 242-246 

Epoch, 246 

Groovings or Scratches, 247 

Lakes, 153 

Sediments, 242 

Streams, 241 
Glaciers, 239 

Geographical Distribution of, 242 

Types of, 239 

Work of, 241 
Globular Lightning, 253 
Gobi, Plateau of, 113 
Gold, Principal Producers of, 323 
Graded Eivers, 141 
Gradient, Barometric, 201 
Gradual Elevations and Subsidences of 

Crust, 84, 85 
Gravitation Theory of Mountain 

Making, 99 
Gravity, 21 
Great Basin, 336 
Plateau of, 102 

Kinghan Mountains, 112 

Lakes of North America, 154, 155 
Green Mountains, 337 
Groovings, Glacial, 247, 248 
Ground Ice, 126 

Moraines, 242 
Guam, Island of, 365 
Guiana, Plateau of, 105 
Gulf of Guinea, Monsoons of, 208 

Stream, 180 
Gulfs and Bays, 167 
Gum Arabic, 287 

H. 

Hachure Lines, 28 
Hail, 246 

Origin of, 237 
Hailstone, Structure of, 236 
Halos, 260 
Hamitic Stock of Caucasian Race, 310, 

311 
Harbors, 82a 



Harmattan, 215 

Hartz Mountains, 109 

Hasheesh, 287 

Hawaiian or Sandwich Islands, 363 

Haze, 224 

Heap or Cumulus Clouds, 226 

Heat Equator, 198 

Latent, 127 

Lightning, 253 

Unit, 127 
Heated Interior, Effects of, 43 
of Earth, Proofs of, 40, 41 
Height of Atmosphere. 190 

of Land, 102 

of Ocean Waves, 168 

of Tidal Wave, 176 
Hemp, 287 

Heredity and Variation, 293 
High Europe, 107 

Lands, 92 

Water, 170 
Hill-side Springs, 130 
Himalayas, 112 
Hindoo- Koosh Mountains, 113 
Hindostan, Mountains of, 112 
Hoar-frost, 223 

Horizontal Distribution of Animal Life, 
294 

Horse Latitudes, 295, 296 

Zones of Vegetation, 272 
Hot or Thermal Springs, 133 
Human Eace, Distribution of, 306 

Unity of, 306 
Humidity, Actual, 222 

Eelative, 222 
Hygrometer, 193, 222 
Hypsometry, 192 

I. 

Iberian Peninsula, Mountains of, 109 
Ice, Anchor, 126 

and Snow, Drainage of, 240 

Fields, 164 

Floes, 164, 246 

Foot, 164 

Ground, 126 

Packs, 164 

Sheets, 164 
Icebergs, 245 

Varieties of, 245 
Ice-cold Water, Latent Heat of, 127 

Stored Heat Energy of, 127 
Ichthyosaurus, 71 
Imaginary Circles, 21, 22 
Immature Eiver Systems, 141 



INDEX. 



391 



India, Plain of, 114 

Eubber, 287 
Indian Corn or Maize, 282 

Ocean, Currents in, 181 
Monsoons of, 208 
Tidal Wave in, 175 
Indigo, 287 

Indo-China, Mountains of, 112 
Inhabitants of Alaska, 358 
Inland Drainage, 129 

of the United States, 338 

or Mediterranean Seas, 167 
' Plains, 93 

Seas and Lakes, Tides in, 176 
Intermont Plateaus, 95 
Invisible Load of Eiver, 142 
Iran, Plateau of, 113 
Iron, Ores of, 322 
Irregular Variation of Needle, 258 
Islands, Continental, 83 

Fluviatile, 145 

of Guam and Tutuila, 365 

of Japan, 84 

of Porto Eico, 361 
Isobaric Charts, 190 
Isobars, 190 
Isoclinal Lines, 258 
Isogonal Lines, 258 
Isothermal Lines, 197 
Italian Peninsula, Mountains of, 109 



Japan Current, 181 

Japhetic Stock of Caucasian Eace, 311 

Jura Mountains, 98, 109 

Jurassic Period, 71 

K. 

Kafla, Plateau of 116 

Karnes, 247 

Kaolin, 326 

Karakorum Mountains, 112 

Kenia, Volcanic Peak of, 116 

Khamsin, 215 

Kilimandjaro. Volcanic Peak of, 116 

Kiolen Mountains, 109 

Kong Mountains, 116 

Kosciusko, Mount, 118 

Krypton, 187 

Kuen-lun Mountains, 112 

Kunchiujunga, 112 



Lacustrine Plains, 93 
Lagoon, 153 



Lahontan Lake, 154, 249 
Lake Basins Due to Changes of Level, 
153 
Due to Landslides and Lava 
Streams, 153 

Systems of the United States, 338 
Lakes Bonneville and Lahontan, 154 

in Delta Districts, 152 

Fluviatile, 145 

Fresh, 152 

Glacial, 153 

in Lower Course of Eiver, 152 

of New Land Areas, 152 

Ox-Bow, 153 

Playa, 154 

Prehistoric, 249 

Salt, 152 

Sea-shore or Lagoon, 153 

Utility of, 157 
Land and Sea Breezes, 207 

and Water Areas, Distribution of, 198 
Articulation of, 166 

Forms of Eelief of, 91, 92 

Horizontal Forms of, 78 

Masses, Continental Contrasts of, 80, 
81 

Peculiarities in Distribution of, 78, 
79 

Slides, 76 

Vertical Forms of, 78 
Lapis-lazuli, 328 

Latent Heat of Ice-cold Water, 127 
Lateral Moraines, 241 
Latitude, Definition of, 23, 24 

Value of Degrees of, 24, 25 
Laurels and Myrtles, Zoues of, 274 
Lava, 44 

Plains, 94 
Law of Precipitations, 223 
Layer or Stratus Clouds, 227 
Lead and Zinc Ores, Deposits of, 324 
Leafless Forests, 278, 279 
Levees of the Mississippi, 143 
Life History of Volcano, 52 
Light, Heat, and Moisture, Geographic 
Effects of 77 

Northern, 254 
Lightning, 252 

Varieties of 252, 253 
Light-year, Definition of, 16 
Lines, Co-tidal, 175 

Isoclinal, 258 

Isogonal, 258 

Isothermal, 197 

of Trend, 80 
Littoral Fauna, 305 



392 



INDEX. 



Llanos of the Orinoco, 106, 273 

Load of Eiver, 142 

Lodes, 320 

Lofty Mountains, 98 

Logwood, 287 

Lombardy, Eiver Plains of, 143, 144 

Looming, 261 

Longitude, Definition of, 23, 24 

Value of Degrees of, 24, 25 
Longitudinal Valleys, 99 
Loo Choo Islands, 84 
Low Europe, 107 

Lands, 92 

Water, 170 
Lower or Plains Course of Eiver, 139 
Lupata Mountains, 116 

M. 

Magnetic Attractions and Eepulsions, 
256 

Declination, 257 

Equator, 258 

Field, 255 

Flux, 255 
Magnetism, 254 
Magnets, 254 

Artificial and Natural, 255 
Maize or Indian Corn, 282 
Malay or Brown Eace, 317 
Malayic Branch of Brown Eace, 317 
Mammoth Cave of Kentucky, 129 
Man, Distribution of, 306 
Mantchuria, Plain of, 114 
Map Projections, 25 
Marginal Plateaus, 95 
Marine Fauna, 304 
Mariner's Compass, 256a 
Marl, 327 
Marsh Lakes, 156 
Marshes, 156 

Mathematical Geography, Definition 
of, 11 

Zones, 35 
Matter, Inorganic, 267 

Organic, 267 
Matterhorn, 107 
Matured Eiver-systems, 141 
Maximum Density of Water, 125 
Meadows, 279 

Mean Annual Isotherms of United 
States, 339 
Eainfall, Chart of, 234 
Temperature, 197 
Meanders, 145 
Medial Moraines, 241 



Mercator's Projection, 25, 26 
Mercurial Barometer, 188 
Meridian, Definition of, 22, 23 
Metallic Thermometer, 193 
Meteorology, 186 
Mesas, 95 
Mesozoic Era, 71 
Meteors, 14 

Mexican Gulf and Caribbean Sea, Mon- 
soons of, 208 
Middle or Valley Course of Eiver, 139 
Mineral Deposits of Alaska, 358 
of Philippine Islands, 361, 362 

Pitch, 326 

Products, Classification of, 322 
Value of, 321 

Springs, 135 

Substances, Varieties of, 321 

Veins, 319 

Varieties of, 320 
Minerals, Definition of, 63 

Distribution of, 319 

Enumeration of Some Important, 
63 
Mining, Hydraulic, 322 
Miocene Epoch, 71 
Mirage, 260, 261 
Mississippi, Alluvial Flats of, 144 

Delta of, 146 

Levees of, 143 
Mistral, 216 
Mists, 22 

Mocambe Mountains, 116 
Mock Moons, 260 

Suns, 260 
Modifiers of Climate, 198 
Mongolian or Yellow Eace, 312 
Monsoon Eegions, 208 
Monsoons, 207 

of Indian Ocean, 208 

of the Gulf of Guinea, 208 
Mont Blanc, 107 
Mont Eosa, 107 
Moon, Phases of, 172 
Moons or Satellites, 16, 17 
Moors, Sphagnum, 280, 281 

Swamp, 280 
Moraine Deposits, 246 
Moraines, Varieties of, 241, 242 
Morasses, 156, 157 
Mount Everest, 112 
Mount McKinley, 102 
Mountain Chain, 96 

Making, Gravitation Theory of, 99 

Passes, 95 

Peaks, 95 



INDEX. 



393 



Mountain System, 9t 

Winds, 209 
Mountains, 95 

Block, 98 

of Denudation, 97 

Dome-shaped, 99 

Embayed, 98 

by Flexure, 98 

by Fracture, 98 

Origin of, 96 

Subtuberant, 99 

of Uplift, 97 
Mudflats, 83 
Multiple or Ribbon Lightning, 253 

N. 

Nanling Mountains, 114 
Natural Bridges, 75 

Nature of Surface, Effect of, on Tem- 
perature of Air, 200 
Neap Tides, 172, 173 
Nearctic Region of Animals, 297, 299 
Nebular Hypothesis, Laplace's, 31 
Needle, Inclination or Dip of, 258 
Variation or Declination of, 257 
Negrillo Branch of Ethiopian Race, 314, 

315 
Negritic Branch of Brown Race, 317 
Negro Branch of Ethiopian Race, 315 
Negroid Branch of Ethiopian Race, 

315 
Nootropic Region of Animals, 299, 300 
Newfoundland, Fogs of, 225 
New Zealand^jeyser Region, 135 
Niagara, Falls of, 138 
Nicaragua Wood, 287 
Nieuveldt Mountains, 116 
Nile, Delta of, 146, 147 
Nimbus or Storm Clouds, 226 
Non-periodical Rain Zones, 231 
North America, Approximate Dimen- 
sions of, 103 
Culminating Point of, 103 
Drainage Systems of, 149 
Glaciers of, 243 
Great Lakes of, 154, 155 
Isolated Water-sheds or Drainage 

Centres of, 150 
Relief Forms of, 100-103 
Salt Lakes of, 155, 156 
Surface Structure of, 100 
Mediterranean Branch of White Race, 
311 
North-easters of the United States, 214 
Northern Light, 254 



Northers of Texas, 216 
Nutmegs, 286 

o. 

Oats, 281 

Oblique Rays of Sun, Heating Power 

of, 194, 195 
Ocean, Aerial, 186 
Currents, Constant, 177 

Effects of, on Temperature of Air, 
200 
Drifts, 179 
Floor, 165 
Ice, 163 
Line of Invariable Temperature of, 

163 
Streams, 179 
Water, Color of, 162 
Composition of, 162 
Density of, 162 

Inequalities in Saltness of, 162 
Temperature of, 162 
Waves, Action of, 77 
Oceanic Areas, 166 
Climate, 199 
Drainage, 129 
Island Chains, 86 
Islands, Classes of, 85, 86 
Movements, 168 
Waves, 168 
Oceans, Boundaries of, 166 
Oil-fields, 326 
Old Plains, 94 
I Plateaus, 95 

River-systems, 141 
Oligocene Epoch, 71 
Olive Oil, 287 
Ooze Deposits, 167 
Opium, 286 
Optical- Phenomena of Atmosphere, 

259 
Ore, Free Milling, 322 
Ores, Metallic, 321 
Oriental Region of Animals, 303 
Origin of Atmospheric Circulation, 202, 
203 
of Constant Ocean Currents, 177, 178 
of Hail, 237 
of Salt Lakes, 156 
of Saltness uf Ocean, 162 
of Winds, 201 
Orinoco, Llanos of, 106 
Orology, 96 

Outlets or Distributaries of Rivers, 152 
Ox-bow Lakes, 153 



394 



INDEX. 



P. 

Pacific Highlands, 335 

Mountain Chains, 336 

Ocean, Currents in, 180, 181 
Greatest Depth of, 166 
Tidal Wave in, 175 
Pago-Pago, Harbor of, 365 
Palaearctic Eegion of Animals, 300, 301 
Palaeontology, 66 
Palseotherium, 71 
Palaeozoic Era, 68 
Palm Oil, 287 

Pampas of the Eio de la Plata, 106 
Pamperos, 216 
Paraselena, 260 
Parasitic Cones, 47 
Parhelia, 260 
Pasco, Plateau of, 105 
Patagonian Archipelago, Islands of, 84 
Pearls, 328 
Peat, 326 

Bogs, 157 
Peculiarities of Continental Beliefs, 99 

of Cyclones, 210, 211 
Pelagic Fauna, 305 
Peling Mountains, 114 
Peneplains, 94 
Pepper, 286 
Period of Coal Plants, 69 

of Mollusks, 68 
Periodical Eain Zones, 230 
Permian Period, 71 
Perpetual Snow, Eegions of, 238 
Persia, Plain of, 114 
Petrifactions, 66 
Petroleum, 325 

By-products of, 326 
Phases of the Moon, 18a 
Philippine Islands, 358-363 

Agricultural Products of, 360, 361 
Area of, 360 
Climate of, 362 
Map of, 359 

Mineral Deposits in, 361, 362 
Principal Islands of, 360, 361 
Philippines, 84, 85 
Phosphorescence, 162 
Photosynthesis, 268 
Physical Climate, 193 

Climatic Zones of the United States, 
339 

Geography, Definition of, 11 

Zones, 197, 198 
Physiographical Animal Barriers, 291 
Physiological Animal Barriers, 292 



Piedmont Glaciers, 237 
Placer Deposits of Gold, 322 
Plain of the Mississippi Valley, 337 
Plains, 93 

Alluvial, 93 

Coastal, 93 

Fluviatile, 93 

Inland, 93 

Lacustrine, 93 

Marine, 93 
Plane of Earth's Orbit, Definition of, 32 
Planets, 14 
Plant Geography, 268 

Groups or Societies, 270 

Growth, Conditions Eequisite for, 269 

Eegions, 277 
Plants, Cultivated, 281 

Yielding Beverages, 285 
Plateau of Arabia, 113 

of Bolivia, 105 

of Brazil, 105 

of Deccan, 113 

of Great Basin, 102 

of Guiana, 105 

of Labrador, 102 

of Pasco, 105 

of Quito, 105 
Plateaus, Broken, 95 

Dissected, 95 

Interment, 95 

Marginal, 95 

Old, 95 

Young, 95 
Platinum, Principal Ore Deposits of, 

325 
Playa Lakes, 154 
Plesiosaurus, 71 

Pluviometer, or Eain Gauge, 232 
Po, Plain of, 110 
Polar Circles, 23 

Currents, Atmospheric, 203 

Projection, 27 

Winds, Generally Dry Character o% 
230 
Eains of, 231 

Zone of Vegetation, 276 

Zones, 206 
Characteristic Climate of, 196 
Political Geography, Definition of, 11 
Popocatepetl, 102 

Porto Eico, Climate and Products of 
365 
Island of, 364 
Position of Mountain Eegion, Effect of 

on Temperature of Air, 200 
Potatoes, 282 



INDEX. 



395 



Pound-degree Fahrenheit, 127 
Prairies, 279 
Precious Stones, 327 
Precipitation, Law of, 223 

of Saline Substances, 156 

Varieties of, 223 
Predominant Mountain System, Com- 
mon, Usage of Term, 100 
Prehistoric Lakes, 249 
Pi'essure, Atmospheric, 188 
Prevailing Westerly Wind Zones, Eaius 
of, 231 
Zones of, 206 
Primary Eaces of Men, 309 

Volcanic Eruptions, 47 
Prime Essentials of Vegetation, 270 
Prismatic Colors of Sunlight, 259 
Proteids, 267 
Protoplasm, 267 
Psychrometer, 222 
Pyrenees Mountains, 107 



Quagmire, 157 
Quaking Bogs, 281 
Quercitron, 287 
Quinine, 287 
Quito, Plateau of, 105 

R. 

Races and Whirlpools, 177 

of Men, 309 
Rafts, 144 
Rain, 228 

Geographical Distribution of, 232, 233 

How Caused, 229 

Quantity of. How Measured, 232 

Zones, Periodical, 230 
Rainbow, Cause of, 259, 260 
Raindrops, Size of, 229 
Rainfall, Distribution of, 229 
Rain-gauge, or Pluviometer, 232 
Rapids and Waterfalls, Formation of, 

138 
Realms of Animal Life, 296 
Red or American Race, 318 
Red River, Raft of, 144 
Reefs, 81 

Eegelation, Action of, in Glaciers, 240 
Regions of Cyclones, 210 

of Perpetual Snow, 238 
Rejuvenated Rivers, 141 
Relative Humidity, 222 

Land and Water Areas of Earth, 77, 
78 



Eelief Forms of Europe, 107 
of North America, 100-103 
of South America, 104-106 
Eevived Rivers, 141 
Revolution of the Earth, 30 
Ribbon or Multiple Lightning, 255 
Eice, 282 

Rills, Definition of, 137 
Rio de la Plata, Pampas of, 106 
River Basin, 137 

Channel, 137 

Channels, Glacial Disturbances of, 249 

Courses, Changes in, 139 

Ferrel's Law Applied to, 145 
or Tracts, 137 

Definition of, 137 

Load of, 75 

Mouth, 137 

Mouths, 140 

Source, 137 

System, 137 

Development of, 148 

Systems, Immature or Young, 141 
Matured or Old, 141 

Terraces, 145 

Transporting Power of, 142 

Valleys, 137 
River-made Plains, 94 
River's Load, 142 
Rivers, Dismembered, 142 

Drowned, 147 

Engrafted, 142 

Graded, 142 

Inundations of, 140 

Rejuvenated, 142 

Revived, 142 
Rivulets, Definition of, 137 
Rock, Definition of, 63 
Rocks, jEolian, 65 

Aqueous, 64 

Basement, 68 

Crystalline, 65 

Fossiliferous, 66 

Fragmental, 65 

Fundamental, 68 

Igneous, 64 

Metam Orphic, 64 

Non-fossiliferous, 66 

Plutonic, 64 

Primitive, 65 

Sedimentary, 64 

Stratified, 65 

Unstratified, 65 

Volcanic, 64 
Rocky Mountains, 335 
Cordillera of, 100 



396 



INDEX. 



Eotation of Earth, Proofs of, 28, 29 
Eotundity of the Earth, Proofs of, 19-21 
Eye, 281 



Sahara, Plateau of, 116, 117 

Sailing Eoutes, 216, 217 

Saline Substances, Precipitation of, 156 

Salt and Alkaline Deserts, 280 

Common, 327 

Lakes, 152 
Origin of, 156 

Plants, 271 

Springs, 136 
Saltness of Ocean, Origin of, 162 
Sand-bars, 81 
Sand-drifts, 81 

Sandwich Islands, Agricultural Produc- 
tions of, 363 
Surface Structure of, 363 

or Hawaiian Islands, 363 
Sapphire, 328 
Sargasso Seas, 181 
Scales, Map, 28 
Scratches, Glacial, 247 
Seas, 168 

Border, 167 

Inland or Mediterranean, 167 

Sargasso, 181 
Sea-shore Lakes, 153 
Secondary Mountain System, Common 
Usage of Term, 100 

Eaces of Men, 309 

Volcanic Eruptions, 47 
Secular Variation of Needle, 258 
Self-recording Barometer, 189, 190 

Thermometer, 194 
Selvas of the Amazon, 106 
Semitic Stock of Caucasian Eace, 311 
Sheet or Fissure Eruptions, Varieties 
of, 53, 54 

Lightning, 253 
Shelves, 165 

Shifting of Wind Zones, 206 
Shoals, 165 
Shore Lines, 81 

Sibiric Branch of Yellow Eace, 313 
Sierra Madre Mountains, 101 
Sierra Nevada and Cascade Eanges, 102 

Eange, 102 
Silicious Springs, 136 
Silt, Deposition of, 142 

or Detritus, 142 
Silurian Period, 68 
Simitic Branch of Yellow Race, 313 



Simoom or Samiel, 215 
Sink-holes, 74 
Sirocco, 215 
Sky, Blue Color of, 260 

Sunset Tints of, 260 
Sleet, 229 
Snow, 237 
Crystals, 237 
Line, 238 

Circumstances Affecting Height of 
. 238 
Mountains, 116 
Societies or Groups of Plants, 270 
Soil, Formation of, 269 
Soils, Classification of, 269 
Solano, 215 
Solar System, Position of, in Space, 18 

Tides, 171 
Solvent Powers of Water, 128 
Soudan, 117 
Sources, Electric, 250 
South America, Approximate Dimen 
sions of, 106 
Culminating Point of, 104 
Drainage Systems of, 150 
Fresh-water Lakes of, 155 
Relief Forms of, 104-106 
Salt Lakes of, 156 
Secondary Mountain Systems of, 10^ 
Surface Structure of, 104 
Mediterranean Branch of Caucasian 
Eace, 310 
Specific Heat, Definition of, 126 

of Water, 126 
Sphagnum Moors, 280, 281 

or Water Moss, 157 
Spheroids, Oblate and Prolate, 1.9 
Spices, Geographic Distribution of, 285 
Spring Tides, 172, 173 
Springs, Acidulous, 136 
Artesian, 130, 131 
Calcareous, 135 
Chalybeate, 136 
Classification of, 132 
Cold, 133 
Constant, 132 
Definition of, 129 
Fissure, 130 
Hill-side, 130 
Hot or Thermal, 133 
Mineral, 135 
Eeservoirs of, 132 
Salt, 136 
Silicious, 136 
Sulphurous, 136 
Temporary, 132 



INDEX. 



397 



stalactites, 75 

Stalactitic Deposits, 136 

Stalagmites, 75 

Stalagmitic Deposits, 136 

Standard Time, 30b 

St. Elmo's Fire, 254 

Staubbach, Falls of, 138 

Steppes, 279 

Stereographic Projection, 26 

Stock Languages, 309 

Stored Heat Energy of Water Vapor, 

127, 128 
Storm, " Eye " of, 209 

or Nimbus Clouds, 227 
Storms, 209 

Stratus or Layer Clouds, 227 
Streams, Underground, 129 
Struggle for Existence, 294 
Sub-arctic Zone of Vegetation, 275 
Submarine Volcanoes, 49 
Subterranean Drainage, 128, 129 

Waters, 129 
Subtropical Zones of Vegetation, 274 
Subtuberaut Mountains, 99 
Sugar Cane, 284 
Sulimau Mountains, 113 
Sulphur, 326, 327 
Sulphurous Springs, 136 
Sunlight, Prismatic Colors of, 259 
Sunset Tints of Sky, 260 
Surface and Upper Atmospheric Cur- 
rents, Interchange of, 204 

Drainage, 128, 129 

Structure of Sandwich Islands, 363 
Survival of the Fittest, Doctrine of, 293 
Svsramp Forests, 279 

Moors, 280 

Thicket, 280 
Swamps, 156 
Swiss Plateau, 109 

T. 

Table Mountain, 116 
Tanganyika Lake, 117 
Tapioca, 284 . 
Tchad Lake, 117 
Tea, 285 

Temperate Latitude or Extra-tropical 
Cyclones, 213, 214 

Zones, Characteristic Climate of, 196 
Temperature, 193 

of Ocean Water, 162 
Temperature Gradient, 197b 
Terminal Moraines, 241 
Theory of Tides, 170 



Thermograph, 194 
Thermometer, 193 

Self-recording, 194 
Thiau Shan and Altai Mountains, 113 
Thibet, Plateau of, 112 
Thunder, 252 
Thunder-storms and Thunder Squalls, 

216 
Tidal Wave, Birthplace of, 173 
Height of, 176 

Waves, 69 
Tide, Ebb, 169 

Flood, 169 
Tides, Cradle of, 173 

Definition of, 169 

Neap, 172, 173 

Solar, 171 

Spring, 172, 173 

Theory of, 170 
Till sheets, 246, 247 
Tin, Principal Ore Deposits of, 325 
Tobacco, 287 
Topaz, 328 
Tornadoes, 212 
Torrens Lake, 118 
Torricelli, 188 

Trade Winds, Zones of, 205 
Transportation and Deposition, 76 
Transverse Valleys, 99 
Transylvanian Mountains, 107, 109 

Plateau, 109 
Travertine, 136 
Trend, Lines of, 80 
Triassic Period, 71 
Tropical Cyclones, 209 

Deserts, 280 

Eegions, Food Plants of, 282, 283 

Zone of Vegetation, 273 
Tropics, 23 

Characteristic Climate of, 196 
Troughs, 165 
Tundras, 114 
Turko-Grecian Peninsula, Mountains 

of, 109 
Turquoise, 328 
Tutuila, Island of, 365 
Twin Continents, 79 
Types of Glaciers, 239 

u. 

Under-currents, 177 
Underground Streams, 129 
Undertow, 169 
United States, Area of, 334 
Climate of, 339 



398 



INDEX. 



United States, Climatic Contrasts of, 
339, 340 
Coast Line of, 334 
Constancy of Climate of, 341 
Drainage Systems of, 338 
Forms of Eelief of, 334, 335 
Gulfs and Bays of, 334 
Islands of. 334 
Mean Annual Isothermal Lines of, 

339 
Peculiarities of Climate of, 339 
Physical Climatic Zones of, 339 
Rainfall in, 341 
Wind Zone of, 341 
Unity of the Human Eace, 306 

Proofs of, 306, 307 
Upper or Mountain Course of Eiver, 

137 
Ural Mountains, 109, 110 
Utility of Currents, 181, 182 
of Lakes, 157 

V. 

Valdai Hills, 110 
Valley Trains, 247 
Valleys, Longitudinal, 99 

Origin of, 99 

Transverse, 99 
Vanilla, 285,286 
Variation or Declination, 257 
Varieties of Glacial Drift Deposits, 246 
Vegetation, Distribution of, 271 

Horizontal Zones of, 272 

Prime Essentials of, 270 

Vertical Distribution of, 276, 277 
Veins, Mineral, 319 

of Infiltration, 320 

of Segregation, 320 
Velocity of Eiver, Causes Determining, 

137 
Vertical Distribution of Animal Life, 
295 
of Vegetation, 276 

Eays of Sun, Heating Povrer of, 194, 
195 
Victoria, Falls of, 138 

Nyanza, 117 
Vindhya Mountains, 113 
Visible Load of Eiver, 142 
Volcanic Ashes or Cinders, 45 

Dykes, 47 

Eruptions, Cause of, 46, 47 
Explosive, 48 
Non-explosive, 48 

Oases or Vapors, 45 



Volcanic Lightning, 253 

Necks, 47, 48 

or Crater Eruptions, 43 
Volcano, Life History of, 52 
Volcanoes, Active, 49 

Extinct, 49 

of Philippine Islands, 362, 363 

Principal Eegions of, 49-51 

Submarine, 49, 51 
Volt, 250 
Vosges Mountains, 109 

w. 

Wake Island, 365 

Warm Temperate Zones of Vegetation, 
274 

Waves, 214 
Water, Circulation of, 124 

Composition of, 125 

Maximum Density of, 125 

Moss, or Sphagnum, 157 

Plants, 270 

Properties of, 125 

Solvent Powers of, 128 

Specific Heat of, 126 

Vapor, Stored Heat Energy of, 127. 
128 
Water-bottle, 165 
Water-falls, Erosion of, 138 
Water-gap, Formation of, 149 
Water-shed, Definition of, 137 
Water-spouts, 213 
Waters, Subterranean, 129 
Waves, Earthquake, 169 

Force of, 169 

Ocean, Height of, 168 

Tidal, 169 
Weather Bureau, 342 

Forecasts, 342 

Indications, 342 
Weathering, Agencies Producing, 73, 
74 

Definition of, 72, 73 
Wells, 129 

Artesian, 131 
Western Continent, Deserts of, 235, 

236 
Wheat, 281 

Whirlpools and Eaces, 177 
White Caps, 169 

Mountains, 337 

or Caucasian Eace, 309 
Wind Corrasion, 76 

Erosion, 76 

Gap, Formation of, 149 



INDEX. 



399 



Wind Transportation, 76 

Zones, 205 

Shifting of, 206 
Winds, Classification of, 204, 205 

Definition of, 201 

Etesian, 216 

Mountain, 208 

Origin of, 201 
Work of Eivers, 142 
Worn-down Mountain Low Lands, 94 



Yablonoi Mountains, 113 
Yams, 284 

Yellow or Mongolian Eace, 312 

Yellowstone National Park, 335 

Geyser Region, 135 



Yosemite, Falls of, 138 
Young Eiver Systems, 141 



Zagros Mountains, 113 
Zig-zag Lightning, 252 
Zinc and Lead Ore, Deposits of, 324 

Blende, 324 
Zone of Calms, Eains of, 230 

of Equatorial Calms, 205 

of the Trades, Eains of, 230 
Zones of the Calms of Cancer and 
Capricorn, 205 

of Prevailing Westerly Winds, 206 

of the Trade Winds, 205 

Physical, 197, 198 
Zoological Geography, 290 



